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 $197.34   10.621%   $218.2995   $218.30   $218.30   $218.30  
  Purchase #2 $205.58   9.495%   $225.0998   $225.10   $225.10   $225.10  
  Purchase #3 $249.28   7.226%   $267.293   $267.29   $267.30   $267.30  
  Purchase #4 $68.75   7.593%   $73.9702   $73.97   $73.95   $74.00  
  Purchase #5 $176.69   6.308%   $187.8356   $187.84   $187.85   $187.80  
  Purchase #6 $139.48   8.677%   $151.5827   $151.58   $151.60   $151.60  
  Purchase #7 $241.41   11.571%   $269.3436   $269.34   $269.35   $269.30  
  7 purchase totals = $1,278.53       $1,393.4244   $1,393.42   $1,393.45   $1,393.40