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 $120.46   11.696%   $134.549   $134.55   $134.55   $134.50  
  Purchase #2 $68.85   11.781%   $76.9612   $76.96   $76.95   $77.00  
  Purchase #3 $118.55   11.811%   $132.5519   $132.55   $132.55   $132.60  
  Purchase #4 $45.35   10.745%   $50.2229   $50.22   $50.20   $50.20  
  Purchase #5 $224.62   8.682%   $244.1215   $244.12   $244.10   $244.10  
  Purchase #6 $26.47   10.657%   $29.2909   $29.29   $29.30   $29.30  
  Purchase #7 $152.74   3.462%   $158.0279   $158.03   $158.05   $158.00  
  7 purchase totals = $757.04       $825.7253   $825.72   $825.70   $825.70