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 $111.26   7.705%   $119.8326   $119.83   $119.85   $119.80  
  Purchase #2 $149.41   6.427%   $159.0126   $159.01   $159.00   $159.00  
  Purchase #3 $77.94   5.838%   $82.4901   $82.49   $82.50   $82.50  
  Purchase #4 $25.31   11.709%   $28.2735   $28.27   $28.25   $28.30  
  Purchase #5 $223.75   10.824%   $247.9687   $247.97   $247.95   $248.00  
  Purchase #6 $182.63   11.370%   $203.395   $203.40   $203.40   $203.40  
  Purchase #7 $102.26   6.377%   $108.7811   $108.78   $108.80   $108.80  
  7 purchase totals = $872.56       $949.7536   $949.75   $949.75   $949.80