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 $54.71   5.288%   $57.6031   $57.60   $57.60   $57.60  
  Purchase #2 $246.30   11.679%   $275.0654   $275.07   $275.05   $275.10  
  Purchase #3 $239.97   13.290%   $271.862   $271.86   $271.85   $271.90  
  Purchase #4 $149.74   11.743%   $167.324   $167.32   $167.30   $167.30  
  Purchase #5 $213.92   9.740%   $234.7558   $234.76   $234.75   $234.80  
  Purchase #6 $135.78   9.273%   $148.3709   $148.37   $148.35   $148.40  
  Purchase #7 $49.37   6.213%   $52.4374   $52.44   $52.45   $52.40  
  7 purchase totals = $1,089.79       $1,207.4186   $1,207.42   $1,207.35   $1,207.50