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 $189.33   6.844%   $202.2877   $202.29   $202.30   $202.30  
  Purchase #2 $48.98   9.426%   $53.5969   $53.60   $53.60   $53.60  
  Purchase #3 $85.35   11.174%   $94.887   $94.89   $94.90   $94.90  
  Purchase #4 $58.30   12.431%   $65.5473   $65.55   $65.55   $65.50  
  Purchase #5 $17.58   4.232%   $18.324   $18.32   $18.30   $18.30  
  Purchase #6 $126.57   9.301%   $138.3423   $138.34   $138.35   $138.30  
  Purchase #7 $217.71   6.265%   $231.3495   $231.35   $231.35   $231.30  
  7 purchase totals = $743.82       $804.3347   $804.34   $804.35   $804.20