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 $56.88   7.326%   $61.047   $61.05   $61.05   $61.00  
  Purchase #2 $92.97   4.253%   $96.924   $96.92   $96.90   $96.90  
  Purchase #3 $156.99   4.758%   $164.4596   $164.46   $164.45   $164.50  
  Purchase #4 $49.44   3.750%   $51.294   $51.29   $51.30   $51.30  
  Purchase #5 $146.63   13.415%   $166.3004   $166.30   $166.30   $166.30  
  Purchase #6 $199.28   12.567%   $224.3235   $224.32   $224.30   $224.30  
  Purchase #7 $165.36   6.510%   $176.1249   $176.12   $176.10   $176.10  
  7 purchase totals = $867.55       $940.4734   $940.46   $940.40   $940.40