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 $222.29   4.851%   $233.0733   $233.07   $233.05   $233.10  
  Purchase #2 $243.79   13.347%   $276.3287   $276.33   $276.35   $276.30  
  Purchase #3 $227.71   3.841%   $236.4563   $236.46   $236.45   $236.50  
  Purchase #4 $86.84   11.378%   $96.7207   $96.72   $96.70   $96.70  
  Purchase #5 $214.26   8.867%   $233.2584   $233.26   $233.25   $233.30  
  Purchase #6 $149.41   5.572%   $157.7351   $157.74   $157.75   $157.70  
  Purchase #7 $26.35   11.820%   $29.4646   $29.46   $29.45   $29.50  
  7 purchase totals = $1,170.65       $1,263.0371   $1,263.04   $1,263.00   $1,263.10