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 $92.95   12.268%   $104.3531   $104.35   $104.35   $104.40  
  Purchase #2 $195.78   4.412%   $204.4178   $204.42   $204.40   $204.40  
  Purchase #3 $174.95   7.509%   $188.087   $188.09   $188.10   $188.10  
  Purchase #4 $127.57   9.302%   $139.4366   $139.44   $139.45   $139.40  
  Purchase #5 $227.53   6.738%   $242.861   $242.86   $242.85   $242.90  
  Purchase #6 $188.90   6.395%   $200.9802   $200.98   $201.00   $201.00  
  Purchase #7 $64.78   12.873%   $73.1191   $73.12   $73.10   $73.10  
  7 purchase totals = $1,072.46       $1,153.2548   $1,153.26   $1,153.25   $1,153.30