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 $22.29   8.822%   $24.2564   $24.26   $24.25   $24.30  
  Purchase #2 $56.59   10.753%   $62.6751   $62.68   $62.70   $62.70  
  Purchase #3 $123.54   13.313%   $139.9869   $139.99   $140.00   $140.00  
  Purchase #4 $178.77   12.773%   $201.6043   $201.60   $201.60   $201.60  
  Purchase #5 $217.28   11.621%   $242.5301   $242.53   $242.55   $242.50  
  Purchase #6 $224.83   11.805%   $251.3712   $251.37   $251.35   $251.40  
  Purchase #7 $79.54   6.493%   $84.7045   $84.70   $84.70   $84.70  
  7 purchase totals = $902.84       $1,007.1285   $1,007.13   $1,007.15   $1,007.20