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 $42.87   12.644%   $48.2905   $48.29   $48.30   $48.30  
  Purchase #2 $147.54   4.479%   $154.1483   $154.15   $154.15   $154.10  
  Purchase #3 $59.33   11.839%   $66.3541   $66.35   $66.35   $66.40  
  Purchase #4 $160.57   13.558%   $182.3401   $182.34   $182.35   $182.30  
  Purchase #5 $49.93   11.245%   $55.5446   $55.54   $55.55   $55.50  
  Purchase #6 $23.37   3.213%   $24.1209   $24.12   $24.10   $24.10  
  Purchase #7 $189.67   3.169%   $195.6806   $195.68   $195.70   $195.70  
  7 purchase totals = $673.28       $726.4791   $726.47   $726.50   $726.40