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 $159.25   5.754%   $168.4132   $168.41   $168.40   $168.40  
  Purchase #2 $196.53   5.256%   $206.8596   $206.86   $206.85   $206.90  
  Purchase #3 $243.89   5.390%   $257.0357   $257.04   $257.05   $257.00  
  Purchase #4 $34.82   3.256%   $35.9537   $35.95   $35.95   $36.00  
  Purchase #5 $154.51   8.573%   $167.7561   $167.76   $167.75   $167.80  
  Purchase #6 $69.29   3.237%   $71.5329   $71.53   $71.55   $71.50  
  Purchase #7 $13.39   8.791%   $14.5671   $14.57   $14.55   $14.60  
  7 purchase totals = $871.68       $922.1183   $922.12   $922.10   $922.20