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 $36.34   12.418%   $40.8527   $40.85   $40.85   $40.90  
  Purchase #2 $210.56   4.130%   $219.2561   $219.26   $219.25   $219.30  
  Purchase #3 $230.97   5.854%   $244.491   $244.49   $244.50   $244.50  
  Purchase #4 $8.28   5.859%   $8.7651   $8.77   $8.75   $8.80  
  Purchase #5 $58.57   12.622%   $65.9627   $65.96   $65.95   $66.00  
  Purchase #6 $202.36   5.362%   $213.2105   $213.21   $213.20   $213.20  
  Purchase #7 $85.76   9.521%   $93.9252   $93.93   $93.95   $93.90  
  7 purchase totals = $832.84       $886.4633   $886.47   $886.45   $886.60