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 $60.42   3.520%   $62.5468   $62.55   $62.55   $62.50  
  Purchase #2 $217.58   12.523%   $244.8275   $244.83   $244.85   $244.80  
  Purchase #3 $63.82   7.856%   $68.8337   $68.83   $68.85   $68.80  
  Purchase #4 $44.89   11.665%   $50.1264   $50.13   $50.15   $50.10  
  Purchase #5 $148.99   4.429%   $155.5888   $155.59   $155.60   $155.60  
  Purchase #6 $144.25   10.228%   $159.0039   $159.00   $159.00   $159.00  
  Purchase #7 $42.35   11.183%   $47.086   $47.09   $47.10   $47.10  
  7 purchase totals = $722.30       $788.0131   $788.02   $788.10   $787.90