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 $238.63   6.166%   $253.3439   $253.34   $253.35   $253.30  
  Purchase #2 $55.73   10.678%   $61.6808   $61.68   $61.70   $61.70  
  Purchase #3 $147.88   7.457%   $158.9074   $158.91   $158.90   $158.90  
  Purchase #4 $198.28   9.731%   $217.5746   $217.57   $217.55   $217.60  
  Purchase #5 $112.34   7.352%   $120.5992   $120.60   $120.60   $120.60  
  Purchase #6 $56.68   13.474%   $64.3171   $64.32   $64.30   $64.30  
  Purchase #7 $62.64   5.445%   $66.0507   $66.05   $66.05   $66.10  
  7 purchase totals = $872.18       $942.4737   $942.47   $942.45   $942.50