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 $221.62   10.829%   $245.6192   $245.62   $245.60   $245.60  
  Purchase #2 $117.98   12.775%   $133.0519   $133.05   $133.05   $133.10  
  Purchase #3 $61.95   11.588%   $69.1288   $69.13   $69.15   $69.10  
  Purchase #4 $86.52   6.256%   $91.9327   $91.93   $91.95   $91.90  
  Purchase #5 $100.74   5.144%   $105.9221   $105.92   $105.90   $105.90  
  Purchase #6 $248.36   3.583%   $257.2587   $257.26   $257.25   $257.30  
  Purchase #7 $156.80   6.196%   $166.5153   $166.52   $166.50   $166.50  
  7 purchase totals = $993.97       $1,069.4287   $1,069.43   $1,069.40   $1,069.40