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 $63.39   8.844%   $68.9962   $69.00   $69.00   $69.00  
  Purchase #2 $189.35   7.664%   $203.8618   $203.86   $203.85   $203.90  
  Purchase #3 $41.57   9.736%   $45.6173   $45.62   $45.60   $45.60  
  Purchase #4 $86.87   13.438%   $98.5436   $98.54   $98.55   $98.50  
  Purchase #5 $149.82   12.639%   $168.7557   $168.76   $168.75   $168.80  
  Purchase #6 $169.43   10.786%   $187.7047   $187.70   $187.70   $187.70  
  Purchase #7 $33.29   4.602%   $34.822   $34.82   $34.80   $34.80  
  7 purchase totals = $733.72       $808.3013   $808.30   $808.25   $808.30