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 $59.93   10.761%   $66.3791   $66.38   $66.40   $66.40  
  Purchase #2 $220.30   11.309%   $245.2137   $245.21   $245.20   $245.20  
  Purchase #3 $71.84   4.767%   $75.2646   $75.26   $75.25   $75.30  
  Purchase #4 $118.42   9.706%   $129.9138   $129.91   $129.90   $129.90  
  Purchase #5 $15.49   11.799%   $17.3177   $17.32   $17.30   $17.30  
  Purchase #6 $185.92   5.704%   $196.5249   $196.52   $196.50   $196.50  
  Purchase #7 $50.73   7.597%   $54.584   $54.58   $54.60   $54.60  
  7 purchase totals = $722.63       $785.1978   $785.18   $785.15   $785.20