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 $215.79   8.746%   $234.663   $234.66   $234.65   $234.70  
  Purchase #2 $151.85   4.119%   $158.1047   $158.10   $158.10   $158.10  
  Purchase #3 $80.99   7.865%   $87.3599   $87.36   $87.35   $87.40  
  Purchase #4 $201.33   10.430%   $222.3287   $222.33   $222.35   $222.30  
  Purchase #5 $242.46   13.503%   $275.1994   $275.20   $275.20   $275.20  
  Purchase #6 $196.30   10.662%   $217.2295   $217.23   $217.25   $217.20  
  Purchase #7 $117.80   4.825%   $123.4839   $123.48   $123.50   $123.50  
  7 purchase totals = $1,206.52       $1,318.3691   $1,318.36   $1,318.40   $1,318.40