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 $63.48   3.262%   $65.5507   $65.55   $65.55   $65.60  
  Purchase #2 $16.97   3.509%   $17.5655   $17.57   $17.55   $17.60  
  Purchase #3 $225.75   4.482%   $235.8681   $235.87   $235.85   $235.90  
  Purchase #4 $9.58   5.540%   $10.1107   $10.11   $10.10   $10.10  
  Purchase #5 $224.78   3.364%   $232.3416   $232.34   $232.35   $232.30  
  Purchase #6 $199.86   5.235%   $210.3227   $210.32   $210.30   $210.30  
  Purchase #7 $239.26   4.852%   $250.8689   $250.87   $250.85   $250.90  
  7 purchase totals = $979.68       $1,022.6282   $1,022.63   $1,022.55   $1,022.70