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 $48.28   8.119%   $52.1999   $52.20   $52.20   $52.20  
  Purchase #2 $87.42   7.437%   $93.9214   $93.92   $93.90   $93.90  
  Purchase #3 $188.61   9.292%   $206.1356   $206.14   $206.15   $206.10  
  Purchase #4 $68.63   6.536%   $73.1157   $73.12   $73.10   $73.10  
  Purchase #5 $23.25   12.304%   $26.1107   $26.11   $26.10   $26.10  
  Purchase #6 $129.77   5.547%   $136.9683   $136.97   $136.95   $137.00  
  Purchase #7 $9.96   9.431%   $10.8993   $10.90   $10.90   $10.90  
  7 purchase totals = $555.92       $599.3509   $599.36   $599.30   $599.30