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 $214.53   5.840%   $227.0586   $227.06   $227.05   $227.10  
  Purchase #2 $40.61   9.371%   $44.4156   $44.42   $44.40   $44.40  
  Purchase #3 $131.91   5.829%   $139.599   $139.60   $139.60   $139.60  
  Purchase #4 $110.29   8.199%   $119.3327   $119.33   $119.35   $119.30  
  Purchase #5 $154.95   10.430%   $171.1113   $171.11   $171.10   $171.10  
  Purchase #6 $146.76   11.348%   $163.4143   $163.41   $163.40   $163.40  
  Purchase #7 $184.94   13.820%   $210.4987   $210.50   $210.50   $210.50  
  7 purchase totals = $983.99       $1,075.4302   $1,075.43   $1,075.40   $1,075.40