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 $65.41   11.632%   $73.0185   $73.02   $73.00   $73.00  
  Purchase #2 $75.49   12.407%   $84.856   $84.86   $84.85   $84.90  
  Purchase #3 $9.68   4.359%   $10.102   $10.10   $10.10   $10.10  
  Purchase #4 $47.62   10.798%   $52.762   $52.76   $52.75   $52.80  
  Purchase #5 $5.31   12.262%   $5.9611   $5.96   $5.95   $6.00  
  Purchase #6 $226.75   6.213%   $240.838   $240.84   $240.85   $240.80  
  Purchase #7 $240.79   6.325%   $256.02   $256.02   $256.00   $256.00  
  7 purchase totals = $671.05       $723.5576   $723.56   $723.50   $723.60