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 $23.91   11.130%   $26.5712   $26.57   $26.55   $26.60  
  Purchase #2 $28.69   13.234%   $32.4868   $32.49   $32.50   $32.50  
  Purchase #3 $30.33   8.468%   $32.8983   $32.90   $32.90   $32.90  
  Purchase #4 $92.45   3.813%   $95.9751   $95.98   $96.00   $96.00  
  Purchase #5 $153.40   4.254%   $159.9256   $159.93   $159.95   $159.90  
  Purchase #6 $62.62   13.474%   $71.0574   $71.06   $71.05   $71.10  
  Purchase #7 $143.91   3.114%   $148.3914   $148.39   $148.40   $148.40  
  7 purchase totals = $535.31       $567.3058   $567.32   $567.35   $567.40