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 $114.53   3.738%   $118.8111   $118.81   $118.80   $118.80  
  Purchase #2 $179.90   12.514%   $202.4127   $202.41   $202.40   $202.40  
  Purchase #3 $164.48   10.228%   $181.303   $181.30   $181.30   $181.30  
  Purchase #4 $77.81   4.137%   $81.029   $81.03   $81.05   $81.00  
  Purchase #5 $37.44   12.532%   $42.132   $42.13   $42.15   $42.10  
  Purchase #6 $71.56   7.565%   $76.9735   $76.97   $76.95   $77.00  
  Purchase #7 $245.43   3.117%   $253.0801   $253.08   $253.10   $253.10  
  7 purchase totals = $891.15       $955.7414   $955.73   $955.75   $955.70