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 $58.52   11.355%   $65.1649   $65.16   $65.15   $65.20  
  Purchase #2 $207.68   4.709%   $217.4597   $217.46   $217.45   $217.50  
  Purchase #3 $10.97   11.286%   $12.2081   $12.21   $12.20   $12.20  
  Purchase #4 $249.28   13.655%   $283.3192   $283.32   $283.30   $283.30  
  Purchase #5 $61.59   4.431%   $64.3191   $64.32   $64.30   $64.30  
  Purchase #6 $216.70   13.479%   $245.909   $245.91   $245.90   $245.90  
  Purchase #7 $149.42   12.265%   $167.7464   $167.75   $167.75   $167.70  
  7 purchase totals = $954.16       $1,056.1264   $1,056.13   $1,056.05   $1,056.10