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 $228.85   9.125%   $249.7326   $249.73   $249.75   $249.70  
  Purchase #2 $64.63   5.810%   $68.385   $68.39   $68.40   $68.40  
  Purchase #3 $207.66   13.274%   $235.2248   $235.22   $235.20   $235.20  
  Purchase #4 $178.82   10.645%   $197.8554   $197.86   $197.85   $197.90  
  Purchase #5 $213.80   5.391%   $225.326   $225.33   $225.35   $225.30  
  Purchase #6 $126.41   5.457%   $133.3082   $133.31   $133.30   $133.30  
  Purchase #7 $155.58   4.266%   $162.217   $162.22   $162.20   $162.20  
  7 purchase totals = $1,175.75       $1,272.0490   $1,272.06   $1,272.05   $1,272.00