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 $238.43   11.108%   $264.9148   $264.91   $264.90   $264.90  
  Purchase #2 $133.41   12.585%   $150.1996   $150.20   $150.20   $150.20  
  Purchase #3 $44.59   6.812%   $47.6275   $47.63   $47.65   $47.60  
  Purchase #4 $233.38   10.318%   $257.4601   $257.46   $257.45   $257.50  
  Purchase #5 $119.91   7.397%   $128.7797   $128.78   $128.80   $128.80  
  Purchase #6 $182.29   11.126%   $202.5716   $202.57   $202.55   $202.60  
  Purchase #7 $92.63   5.821%   $98.022   $98.02   $98.00   $98.00  
  7 purchase totals = $1,044.64       $1,149.5753   $1,149.57   $1,149.55   $1,149.60