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 $124.53   8.203%   $134.7452   $134.75   $134.75   $134.70  
  Purchase #2 $185.43   7.509%   $199.3539   $199.35   $199.35   $199.40  
  Purchase #3 $62.93   6.239%   $66.8562   $66.86   $66.85   $66.90  
  Purchase #4 $120.40   10.151%   $132.6218   $132.62   $132.60   $132.60  
  Purchase #5 $171.68   12.860%   $193.758   $193.76   $193.75   $193.80  
  Purchase #6 $130.28   6.297%   $138.4837   $138.48   $138.50   $138.50  
  Purchase #7 $138.78   10.684%   $153.6073   $153.61   $153.60   $153.60  
  7 purchase totals = $934.03       $1,019.4261   $1,019.43   $1,019.40   $1,019.50