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 $56.62   7.605%   $60.926   $60.93   $60.95   $60.90  
  Purchase #2 $87.52   6.685%   $93.3707   $93.37   $93.35   $93.40  
  Purchase #3 $170.54   13.849%   $194.1581   $194.16   $194.15   $194.20  
  Purchase #4 $86.54   7.271%   $92.8323   $92.83   $92.85   $92.80  
  Purchase #5 $161.73   8.793%   $175.9509   $175.95   $175.95   $176.00  
  Purchase #6 $190.89   10.736%   $211.384   $211.38   $211.40   $211.40  
  Purchase #7 $50.33   3.678%   $52.1811   $52.18   $52.20   $52.20  
  7 purchase totals = $804.17       $880.8031   $880.80   $880.85   $880.90