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 $61.77   11.178%   $68.6747   $68.67   $68.65   $68.70  
  Purchase #2 $133.95   9.148%   $146.2037   $146.20   $146.20   $146.20  
  Purchase #3 $15.93   8.346%   $17.2595   $17.26   $17.25   $17.30  
  Purchase #4 $57.52   3.657%   $59.6235   $59.62   $59.60   $59.60  
  Purchase #5 $144.96   10.541%   $160.2402   $160.24   $160.25   $160.20  
  Purchase #6 $188.98   8.737%   $205.4912   $205.49   $205.50   $205.50  
  Purchase #7 $16.97   5.185%   $17.8499   $17.85   $17.85   $17.80  
  7 purchase totals = $620.08       $675.3427   $675.33   $675.30   $675.30