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 $250.37   5.666%   $264.556   $264.56   $264.55   $264.60  
  Purchase #2 $177.59   5.435%   $187.242   $187.24   $187.25   $187.20  
  Purchase #3 $156.74   8.732%   $170.4265   $170.43   $170.45   $170.40  
  Purchase #4 $35.74   7.613%   $38.4609   $38.46   $38.45   $38.50  
  Purchase #5 $225.56   7.840%   $243.2439   $243.24   $243.25   $243.20  
  Purchase #6 $113.92   13.589%   $129.4006   $129.40   $129.40   $129.40  
  Purchase #7 $206.62   13.664%   $234.8526   $234.85   $234.85   $234.90  
  7 purchase totals = $1,166.54       $1,268.1825   $1,268.18   $1,268.20   $1,268.20