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 $8.84   8.472%   $9.5889   $9.59   $9.60   $9.60  
  Purchase #2 $194.43   6.705%   $207.4665   $207.47   $207.45   $207.50  
  Purchase #3 $210.42   7.809%   $226.8517   $226.85   $226.85   $226.90  
  Purchase #4 $25.62   7.692%   $27.5907   $27.59   $27.60   $27.60  
  Purchase #5 $149.52   4.411%   $156.1153   $156.12   $156.10   $156.10  
  Purchase #6 $182.96   13.787%   $208.1847   $208.18   $208.20   $208.20  
  Purchase #7 $104.47   3.103%   $107.7117   $107.71   $107.70   $107.70  
  7 purchase totals = $876.26       $943.5095   $943.51   $943.50   $943.60