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 $185.42   11.766%   $207.2365   $207.24   $207.25   $207.20  
  Purchase #2 $73.31   3.790%   $76.0884   $76.09   $76.10   $76.10  
  Purchase #3 $202.42   4.226%   $210.9743   $210.97   $210.95   $211.00  
  Purchase #4 $180.51   8.146%   $195.2143   $195.21   $195.20   $195.20  
  Purchase #5 $236.41   13.227%   $267.68   $267.68   $267.70   $267.70  
  Purchase #6 $79.28   5.400%   $83.5611   $83.56   $83.55   $83.60  
  Purchase #7 $190.61   5.665%   $201.4081   $201.41   $201.40   $201.40  
  7 purchase totals = $1,147.96       $1,242.1627   $1,242.16   $1,242.15   $1,242.20