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 $51.78   12.640%   $58.325   $58.33   $58.35   $58.30  
  Purchase #2 $119.78   10.569%   $132.4395   $132.44   $132.45   $132.40  
  Purchase #3 $164.62   10.596%   $182.0631   $182.06   $182.05   $182.10  
  Purchase #4 $73.92   12.256%   $82.9796   $82.98   $83.00   $83.00  
  Purchase #5 $35.31   10.814%   $39.1284   $39.13   $39.15   $39.10  
  Purchase #6 $212.83   9.523%   $233.0978   $233.10   $233.10   $233.10  
  Purchase #7 $241.37   11.726%   $269.673   $269.67   $269.65   $269.70  
  7 purchase totals = $899.61       $997.7064   $997.71   $997.75   $997.70