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 $188.32   13.609%   $213.9485   $213.95   $213.95   $213.90  
  Purchase #2 $184.47   7.117%   $197.5987   $197.60   $197.60   $197.60  
  Purchase #3 $116.92   12.688%   $131.7548   $131.75   $131.75   $131.80  
  Purchase #4 $248.82   8.593%   $270.2011   $270.20   $270.20   $270.20  
  Purchase #5 $156.75   12.485%   $176.3202   $176.32   $176.30   $176.30  
  Purchase #6 $32.88   11.300%   $36.5954   $36.60   $36.60   $36.60  
  Purchase #7 $220.96   3.461%   $228.6074   $228.61   $228.60   $228.60  
  7 purchase totals = $1,149.12       $1,255.0261   $1,255.03   $1,255.00   $1,255.00