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 $11.57   13.657%   $13.1501   $13.15   $13.15   $13.20  
  Purchase #2 $32.56   8.574%   $35.3517   $35.35   $35.35   $35.40  
  Purchase #3 $14.48   11.408%   $16.1319   $16.13   $16.15   $16.10  
  Purchase #4 $205.35   5.154%   $215.9337   $215.93   $215.95   $215.90  
  Purchase #5 $71.32   6.869%   $76.219   $76.22   $76.20   $76.20  
  Purchase #6 $185.45   11.510%   $206.7953   $206.80   $206.80   $206.80  
  Purchase #7 $149.32   10.538%   $165.0553   $165.06   $165.05   $165.10  
  7 purchase totals = $670.05       $728.6370   $728.64   $728.65   $728.70