Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.38   11.623%   $271.6681   $271.67   $271.65   $271.70  
  Purchase #2 $223.41   10.489%   $246.8435   $246.84   $246.85   $246.80  
  Purchase #3 $213.97   11.193%   $237.9197   $237.92   $237.90   $237.90  
  Purchase #4 $102.69   5.233%   $108.0638   $108.06   $108.05   $108.10  
  Purchase #5 $248.25   11.765%   $277.4566   $277.46   $277.45   $277.50  
  Purchase #6 $119.69   8.359%   $129.6949   $129.69   $129.70   $129.70  
  Purchase #7 $154.85   10.806%   $171.5831   $171.58   $171.60   $171.60  
  7 purchase totals = $1,306.24       $1,443.2297   $1,443.22   $1,443.20   $1,443.30