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 $191.53   13.370%   $217.1376   $217.14   $217.15   $217.10  
  Purchase #2 $109.47   6.827%   $116.9435   $116.94   $116.95   $116.90  
  Purchase #3 $80.67   3.794%   $83.7306   $83.73   $83.75   $83.70  
  Purchase #4 $148.30   7.795%   $159.86   $159.86   $159.85   $159.90  
  Purchase #5 $227.71   8.265%   $246.5302   $246.53   $246.55   $246.50  
  Purchase #6 $44.52   5.584%   $47.006   $47.01   $47.00   $47.00  
  Purchase #7 $20.50   11.759%   $22.9106   $22.91   $22.90   $22.90  
  7 purchase totals = $822.70       $894.1185   $894.12   $894.15   $894.00