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 $64.93   13.350%   $73.5982   $73.60   $73.60   $73.60  
  Purchase #2 $139.74   9.478%   $152.9846   $152.98   $153.00   $153.00  
  Purchase #3 $92.36   12.534%   $103.9364   $103.94   $103.95   $103.90  
  Purchase #4 $241.63   8.595%   $262.3981   $262.40   $262.40   $262.40  
  Purchase #5 $119.61   11.688%   $133.59   $133.59   $133.60   $133.60  
  Purchase #6 $195.94   4.255%   $204.2772   $204.28   $204.30   $204.30  
  Purchase #7 $229.94   5.269%   $242.0555   $242.06   $242.05   $242.10  
  7 purchase totals = $1,084.15       $1,172.8400   $1,172.85   $1,172.90   $1,172.90