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 $191.78   8.225%   $207.5539   $207.55   $207.55   $207.60  
  Purchase #2 $225.95   5.568%   $238.5309   $238.53   $238.55   $238.50  
  Purchase #3 $6.50   8.646%   $7.062   $7.06   $7.05   $7.10  
  Purchase #4 $143.45   9.549%   $157.148   $157.15   $157.15   $157.10  
  Purchase #5 $101.73   4.502%   $106.3099   $106.31   $106.30   $106.30  
  Purchase #6 $118.94   12.338%   $133.6148   $133.61   $133.60   $133.60  
  Purchase #7 $208.66   8.824%   $227.0722   $227.07   $227.05   $227.10  
  7 purchase totals = $997.01       $1,077.2917   $1,077.28   $1,077.25   $1,077.30