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 $166.50   12.283%   $186.9512   $186.95   $186.95   $187.00  
  Purchase #2 $190.63   12.341%   $214.1556   $214.16   $214.15   $214.20  
  Purchase #3 $247.50   9.774%   $271.6907   $271.69   $271.70   $271.70  
  Purchase #4 $62.71   10.499%   $69.2939   $69.29   $69.30   $69.30  
  Purchase #5 $124.29   7.770%   $133.9473   $133.95   $133.95   $133.90  
  Purchase #6 $244.82   11.410%   $272.754   $272.75   $272.75   $272.80  
  Purchase #7 $90.31   9.182%   $98.6023   $98.60   $98.60   $98.60  
  7 purchase totals = $1,126.76       $1,247.3950   $1,247.39   $1,247.40   $1,247.50