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 $247.73   6.492%   $263.8126   $263.81   $263.80   $263.80  
  Purchase #2 $136.82   9.189%   $149.3924   $149.39   $149.40   $149.40  
  Purchase #3 $138.42   11.230%   $153.9646   $153.96   $153.95   $154.00  
  Purchase #4 $24.64   13.424%   $27.9477   $27.95   $27.95   $27.90  
  Purchase #5 $110.80   13.429%   $125.6793   $125.68   $125.70   $125.70  
  Purchase #6 $143.42   6.294%   $152.4469   $152.45   $152.45   $152.40  
  Purchase #7 $84.99   6.674%   $90.6622   $90.66   $90.65   $90.70  
  7 purchase totals = $886.82       $963.9057   $963.90   $963.90   $963.90