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 $58.54   10.428%   $64.6446   $64.64   $64.65   $64.60  
  Purchase #2 $190.60   13.714%   $216.7389   $216.74   $216.75   $216.70  
  Purchase #3 $86.72   5.141%   $91.1783   $91.18   $91.20   $91.20  
  Purchase #4 $96.35   10.436%   $106.4051   $106.41   $106.40   $106.40  
  Purchase #5 $67.44   4.690%   $70.6029   $70.60   $70.60   $70.60  
  Purchase #6 $221.62   13.382%   $251.2772   $251.28   $251.30   $251.30  
  Purchase #7 $208.26   6.345%   $221.4741   $221.47   $221.45   $221.50  
  7 purchase totals = $929.53       $1,022.3211   $1,022.32   $1,022.35   $1,022.30