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 $59.74   11.770%   $66.7714   $66.77   $66.75   $66.80  
  Purchase #2 $5.26   8.267%   $5.6948   $5.69   $5.70   $5.70  
  Purchase #3 $182.59   12.530%   $205.4685   $205.47   $205.45   $205.50  
  Purchase #4 $108.93   9.141%   $118.8873   $118.89   $118.90   $118.90  
  Purchase #5 $36.33   11.648%   $40.5617   $40.56   $40.55   $40.60  
  Purchase #6 $67.77   9.139%   $73.9635   $73.96   $73.95   $74.00  
  Purchase #7 $167.65   11.767%   $187.3774   $187.38   $187.40   $187.40  
  7 purchase totals = $628.27       $698.7246   $698.72   $698.70   $698.90