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 $239.46   13.475%   $271.7272   $271.73   $271.75   $271.70  
  Purchase #2 $23.75   6.528%   $25.3004   $25.30   $25.30   $25.30  
  Purchase #3 $112.85   13.476%   $128.0577   $128.06   $128.05   $128.10  
  Purchase #4 $83.66   6.668%   $89.2384   $89.24   $89.25   $89.20  
  Purchase #5 $157.26   11.404%   $175.1939   $175.19   $175.20   $175.20  
  Purchase #6 $235.91   5.613%   $249.1516   $249.15   $249.15   $249.20  
  Purchase #7 $213.75   10.804%   $236.8436   $236.84   $236.85   $236.80  
  7 purchase totals = $1,066.64       $1,175.5128   $1,175.51   $1,175.55   $1,175.50