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 $59.47   11.600%   $66.3685   $66.37   $66.35   $66.40  
  Purchase #2 $76.60   12.251%   $85.9843   $85.98   $86.00   $86.00  
  Purchase #3 $230.67   12.833%   $260.2719   $260.27   $260.25   $260.30  
  Purchase #4 $68.33   12.653%   $76.9758   $76.98   $77.00   $77.00  
  Purchase #5 $171.90   13.344%   $194.8383   $194.84   $194.85   $194.80  
  Purchase #6 $202.84   11.618%   $226.406   $226.41   $226.40   $226.40  
  Purchase #7 $30.32   9.527%   $33.2086   $33.21   $33.20   $33.20  
  7 purchase totals = $840.13       $944.0534   $944.06   $944.05   $944.10