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 $160.93   13.620%   $182.8487   $182.85   $182.85   $182.80  
  Purchase #2 $73.69   7.590%   $79.2831   $79.28   $79.30   $79.30  
  Purchase #3 $50.65   9.581%   $55.5028   $55.50   $55.50   $55.50  
  Purchase #4 $151.87   8.457%   $164.7136   $164.71   $164.70   $164.70  
  Purchase #5 $62.27   3.639%   $64.536   $64.54   $64.55   $64.50  
  Purchase #6 $110.93   6.294%   $117.9119   $117.91   $117.90   $117.90  
  Purchase #7 $248.53   13.186%   $281.3012   $281.30   $281.30   $281.30  
  7 purchase totals = $858.87       $946.0973   $946.09   $946.10   $946.00