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 $146.89   8.667%   $159.621   $159.62   $159.60   $159.60  
  Purchase #2 $181.97   13.383%   $206.323   $206.32   $206.30   $206.30  
  Purchase #3 $68.70   8.410%   $74.4777   $74.48   $74.50   $74.50  
  Purchase #4 $237.91   7.573%   $255.9269   $255.93   $255.95   $255.90  
  Purchase #5 $25.39   10.715%   $28.1105   $28.11   $28.10   $28.10  
  Purchase #6 $167.41   11.212%   $186.18   $186.18   $186.20   $186.20  
  Purchase #7 $73.57   3.140%   $75.8801   $75.88   $75.90   $75.90  
  7 purchase totals = $901.84       $986.5192   $986.52   $986.55   $986.50