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 $164.68   10.521%   $182.006   $182.01   $182.00   $182.00  
  Purchase #2 $33.94   8.206%   $36.7251   $36.73   $36.75   $36.70  
  Purchase #3 $56.45   7.616%   $60.7492   $60.75   $60.75   $60.70  
  Purchase #4 $91.98   10.658%   $101.7832   $101.78   $101.80   $101.80  
  Purchase #5 $166.29   13.281%   $188.375   $188.38   $188.40   $188.40  
  Purchase #6 $47.60   13.308%   $53.9346   $53.93   $53.95   $53.90  
  Purchase #7 $96.35   11.460%   $107.3917   $107.39   $107.40   $107.40  
  7 purchase totals = $657.29       $730.9648   $730.97   $731.05   $730.90