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 $75.82   11.649%   $84.6523   $84.65   $84.65   $84.70  
  Purchase #2 $86.55   9.731%   $94.9722   $94.97   $94.95   $95.00  
  Purchase #3 $195.41   11.158%   $217.2138   $217.21   $217.20   $217.20  
  Purchase #4 $21.74   10.650%   $24.0553   $24.06   $24.05   $24.10  
  Purchase #5 $129.42   13.196%   $146.4983   $146.50   $146.50   $146.50  
  Purchase #6 $154.48   12.855%   $174.3384   $174.34   $174.35   $174.30  
  Purchase #7 $10.31   8.208%   $11.1562   $11.16   $11.15   $11.20  
  7 purchase totals = $673.73       $752.8865   $752.89   $752.85   $753.00