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 $125.63   12.178%   $140.9292   $140.93   $140.95   $140.90  
  Purchase #2 $195.46   3.724%   $202.7389   $202.74   $202.75   $202.70  
  Purchase #3 $39.35   5.552%   $41.5347   $41.53   $41.55   $41.50  
  Purchase #4 $210.57   6.736%   $224.754   $224.75   $224.75   $224.80  
  Purchase #5 $164.40   5.819%   $173.9664   $173.97   $173.95   $174.00  
  Purchase #6 $197.32   9.184%   $215.4419   $215.44   $215.45   $215.40  
  Purchase #7 $63.73   7.562%   $68.5493   $68.55   $68.55   $68.50  
  7 purchase totals = $996.46       $1,067.9144   $1,067.91   $1,067.95   $1,067.80