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 $22.85   3.727%   $23.7016   $23.70   $23.70   $23.70  
  Purchase #2 $221.52   11.480%   $246.9505   $246.95   $246.95   $247.00  
  Purchase #3 $81.94   9.206%   $89.4834   $89.48   $89.50   $89.50  
  Purchase #4 $190.77   7.680%   $205.4211   $205.42   $205.40   $205.40  
  Purchase #5 $212.94   5.619%   $224.9051   $224.91   $224.90   $224.90  
  Purchase #6 $23.84   7.149%   $25.5443   $25.54   $25.55   $25.50  
  Purchase #7 $46.45   10.603%   $51.3751   $51.38   $51.40   $51.40  
  7 purchase totals = $800.31       $867.3811   $867.38   $867.40   $867.40