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 $178.63   13.623%   $202.9648   $202.96   $202.95   $203.00  
  Purchase #2 $68.75   4.129%   $71.5887   $71.59   $71.60   $71.60  
  Purchase #3 $24.78   4.625%   $25.9261   $25.93   $25.95   $25.90  
  Purchase #4 $201.91   11.311%   $224.748   $224.75   $224.75   $224.70  
  Purchase #5 $102.49   8.726%   $111.4333   $111.43   $111.45   $111.40  
  Purchase #6 $178.96   11.508%   $199.5547   $199.55   $199.55   $199.60  
  Purchase #7 $103.75   13.173%   $117.417   $117.42   $117.40   $117.40  
  7 purchase totals = $859.27       $953.6326   $953.63   $953.65   $953.60