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 $228.38   11.297%   $254.1801   $254.18   $254.20   $254.20  
  Purchase #2 $176.58   6.732%   $188.4674   $188.47   $188.45   $188.50  
  Purchase #3 $102.59   11.584%   $114.474   $114.47   $114.45   $114.50  
  Purchase #4 $184.99   6.609%   $197.216   $197.22   $197.20   $197.20  
  Purchase #5 $104.77   12.835%   $118.2172   $118.22   $118.20   $118.20  
  Purchase #6 $221.55   9.647%   $242.9229   $242.92   $242.90   $242.90  
  Purchase #7 $49.58   4.587%   $51.8542   $51.85   $51.85   $51.90  
  7 purchase totals = $1,068.44       $1,167.3318   $1,167.33   $1,167.25   $1,167.40