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 $58.61   12.804%   $66.1144   $66.11   $66.10   $66.10  
  Purchase #2 $194.94   5.148%   $204.9755   $204.98   $205.00   $205.00  
  Purchase #3 $117.90   12.175%   $132.2543   $132.25   $132.25   $132.30  
  Purchase #4 $190.69   8.841%   $207.5489   $207.55   $207.55   $207.50  
  Purchase #5 $88.41   10.122%   $97.3589   $97.36   $97.35   $97.40  
  Purchase #6 $138.86   7.142%   $148.7774   $148.78   $148.80   $148.80  
  Purchase #7 $212.66   10.286%   $234.5342   $234.53   $234.55   $234.50  
  7 purchase totals = $1,002.07       $1,091.5636   $1,091.56   $1,091.60   $1,091.60