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 $248.69   7.386%   $267.0582   $267.06   $267.05   $267.10  
  Purchase #2 $199.41   12.619%   $224.5735   $224.57   $224.55   $224.60  
  Purchase #3 $44.64   6.482%   $47.5336   $47.53   $47.55   $47.50  
  Purchase #4 $26.48   12.256%   $29.7254   $29.73   $29.75   $29.70  
  Purchase #5 $65.61   5.628%   $69.3025   $69.30   $69.30   $69.30  
  Purchase #6 $94.64   8.586%   $102.7658   $102.77   $102.75   $102.80  
  Purchase #7 $221.99   13.294%   $251.5014   $251.50   $251.50   $251.50  
  7 purchase totals = $901.46       $992.4604   $992.46   $992.45   $992.50