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 $36.32   5.465%   $38.3049   $38.30   $38.30   $38.30  
  Purchase #2 $60.81   8.544%   $66.0056   $66.01   $66.00   $66.00  
  Purchase #3 $8.48   8.762%   $9.223   $9.22   $9.20   $9.20  
  Purchase #4 $84.25   3.111%   $86.871   $86.87   $86.85   $86.90  
  Purchase #5 $163.50   9.214%   $178.5649   $178.56   $178.55   $178.60  
  Purchase #6 $82.83   12.673%   $93.327   $93.33   $93.35   $93.30  
  Purchase #7 $21.93   10.150%   $24.1559   $24.16   $24.15   $24.20  
  7 purchase totals = $458.12       $496.4523   $496.45   $496.40   $496.50