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 $236.46   5.586%   $249.6687   $249.67   $249.65   $249.70  
  Purchase #2 $235.71   13.127%   $266.6517   $266.65   $266.65   $266.70  
  Purchase #3 $119.70   9.717%   $131.3312   $131.33   $131.35   $131.30  
  Purchase #4 $211.97   10.266%   $233.7308   $233.73   $233.75   $233.70  
  Purchase #5 $134.90   8.495%   $146.3598   $146.36   $146.35   $146.40  
  Purchase #6 $191.40   6.484%   $203.8104   $203.81   $203.80   $203.80  
  Purchase #7 $67.98   8.394%   $73.6862   $73.69   $73.70   $73.70  
  7 purchase totals = $1,198.12       $1,305.2388   $1,305.24   $1,305.25   $1,305.30