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 $61.53   11.332%   $68.5026   $68.50   $68.50   $68.50  
  Purchase #2 $217.52   13.105%   $246.026   $246.03   $246.05   $246.00  
  Purchase #3 $93.40   3.485%   $96.655   $96.66   $96.65   $96.70  
  Purchase #4 $199.33   6.480%   $212.2466   $212.25   $212.25   $212.20  
  Purchase #5 $153.64   6.788%   $164.0691   $164.07   $164.05   $164.10  
  Purchase #6 $37.26   6.692%   $39.7534   $39.75   $39.75   $39.80  
  Purchase #7 $68.92   4.371%   $71.9325   $71.93   $71.95   $71.90  
  7 purchase totals = $831.60       $899.1852   $899.19   $899.20   $899.20