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 $199.83   3.108%   $206.0407   $206.04   $206.05   $206.00  
  Purchase #2 $185.27   4.187%   $193.0273   $193.03   $193.05   $193.00  
  Purchase #3 $53.35   8.721%   $58.0027   $58.00   $58.00   $58.00  
  Purchase #4 $66.90   10.741%   $74.0857   $74.09   $74.10   $74.10  
  Purchase #5 $157.25   10.813%   $174.2534   $174.25   $174.25   $174.30  
  Purchase #6 $90.50   4.112%   $94.2214   $94.22   $94.20   $94.20  
  Purchase #7 $215.51   4.203%   $224.5679   $224.57   $224.55   $224.60  
  7 purchase totals = $968.61       $1,024.1991   $1,024.20   $1,024.20   $1,024.20