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 $83.82   11.473%   $93.4367   $93.44   $93.45   $93.40  
  Purchase #2 $140.43   9.160%   $153.2934   $153.29   $153.30   $153.30  
  Purchase #3 $28.78   4.456%   $30.0624   $30.06   $30.05   $30.10  
  Purchase #4 $164.65   5.395%   $173.5329   $173.53   $173.55   $173.50  
  Purchase #5 $232.83   12.223%   $261.2888   $261.29   $261.30   $261.30  
  Purchase #6 $204.58   11.417%   $227.9369   $227.94   $227.95   $227.90  
  Purchase #7 $141.88   13.117%   $160.4904   $160.49   $160.50   $160.50  
  7 purchase totals = $996.97       $1,100.0415   $1,100.04   $1,100.10   $1,100.00