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 $58.39   11.864%   $65.3174   $65.32   $65.30   $65.30  
  Purchase #2 $240.67   12.405%   $270.5251   $270.53   $270.55   $270.50  
  Purchase #3 $10.61   3.382%   $10.9688   $10.97   $10.95   $11.00  
  Purchase #4 $18.58   4.665%   $19.4468   $19.45   $19.45   $19.40  
  Purchase #5 $46.61   11.578%   $52.0065   $52.01   $52.00   $52.00  
  Purchase #6 $118.37   3.128%   $122.0726   $122.07   $122.05   $122.10  
  Purchase #7 $241.95   13.323%   $274.185   $274.19   $274.20   $274.20  
  7 purchase totals = $735.18       $814.5222   $814.54   $814.50   $814.50