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 $59.79   4.182%   $62.2904   $62.29   $62.30   $62.30  
  Purchase #2 $216.44   9.824%   $237.7031   $237.70   $237.70   $237.70  
  Purchase #3 $48.79   6.389%   $51.9072   $51.91   $51.90   $51.90  
  Purchase #4 $238.57   10.865%   $264.4906   $264.49   $264.50   $264.50  
  Purchase #5 $16.27   12.711%   $18.3381   $18.34   $18.35   $18.30  
  Purchase #6 $166.84   10.423%   $184.2297   $184.23   $184.25   $184.20  
  Purchase #7 $76.71   7.229%   $82.2554   $82.26   $82.25   $82.30  
  7 purchase totals = $823.41       $901.2145   $901.22   $901.25   $901.20