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 $142.28   12.723%   $160.3823   $160.38   $160.40   $160.40  
  Purchase #2 $173.73   10.805%   $192.5015   $192.50   $192.50   $192.50  
  Purchase #3 $74.91   10.809%   $83.007   $83.01   $83.00   $83.00  
  Purchase #4 $148.94   4.231%   $155.2417   $155.24   $155.25   $155.20  
  Purchase #5 $109.43   6.852%   $116.9281   $116.93   $116.95   $116.90  
  Purchase #6 $123.46   7.866%   $133.1714   $133.17   $133.15   $133.20  
  Purchase #7 $85.55   7.439%   $91.9141   $91.91   $91.90   $91.90  
  7 purchase totals = $858.30       $933.1461   $933.14   $933.15   $933.10