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 $238.65   7.793%   $257.248   $257.25   $257.25   $257.20  
  Purchase #2 $40.38   3.779%   $41.906   $41.91   $41.90   $41.90  
  Purchase #3 $179.69   12.273%   $201.7434   $201.74   $201.75   $201.70  
  Purchase #4 $135.33   3.429%   $139.9705   $139.97   $139.95   $140.00  
  Purchase #5 $141.82   11.623%   $158.3037   $158.30   $158.30   $158.30  
  Purchase #6 $79.97   5.598%   $84.4467   $84.45   $84.45   $84.40  
  Purchase #7 $11.51   6.383%   $12.2447   $12.24   $12.25   $12.20  
  7 purchase totals = $827.35       $895.8630   $895.86   $895.85   $895.70