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 $88.95   13.163%   $100.6585   $100.66   $100.65   $100.70  
  Purchase #2 $93.48   4.161%   $97.3697   $97.37   $97.35   $97.40  
  Purchase #3 $216.62   11.104%   $240.6735   $240.67   $240.65   $240.70  
  Purchase #4 $52.39   11.804%   $58.5741   $58.57   $58.55   $58.60  
  Purchase #5 $195.85   5.163%   $205.9617   $205.96   $205.95   $206.00  
  Purchase #6 $23.26   7.176%   $24.9291   $24.93   $24.95   $24.90  
  Purchase #7 $193.47   13.681%   $219.9386   $219.94   $219.95   $219.90  
  7 purchase totals = $864.02       $948.1052   $948.10   $948.05   $948.20