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 $53.71   13.463%   $60.941   $60.94   $60.95   $60.90  
  Purchase #2 $190.89   5.274%   $200.9575   $200.96   $200.95   $201.00  
  Purchase #3 $230.36   5.313%   $242.599   $242.60   $242.60   $242.60  
  Purchase #4 $95.60   10.483%   $105.6217   $105.62   $105.60   $105.60  
  Purchase #5 $16.43   13.353%   $18.6239   $18.62   $18.60   $18.60  
  Purchase #6 $29.67   12.375%   $33.3417   $33.34   $33.35   $33.30  
  Purchase #7 $244.35   9.750%   $268.1741   $268.17   $268.15   $268.20  
  7 purchase totals = $861.01       $930.2589   $930.25   $930.20   $930.20