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 $221.51   11.282%   $246.5008   $246.50   $246.50   $246.50  
  Purchase #2 $154.92   5.436%   $163.3415   $163.34   $163.35   $163.30  
  Purchase #3 $113.88   9.384%   $124.5665   $124.57   $124.55   $124.60  
  Purchase #4 $108.64   6.436%   $115.6321   $115.63   $115.65   $115.60  
  Purchase #5 $131.31   7.512%   $141.174   $141.17   $141.15   $141.20  
  Purchase #6 $230.51   9.865%   $253.2498   $253.25   $253.25   $253.20  
  Purchase #7 $71.46   11.719%   $79.8344   $79.83   $79.85   $79.80  
  7 purchase totals = $1,032.23       $1,124.2991   $1,124.29   $1,124.30   $1,124.20