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 $250.62   13.716%   $284.995   $285.00   $285.00   $285.00  
  Purchase #2 $86.27   6.435%   $91.8215   $91.82   $91.80   $91.80  
  Purchase #3 $162.57   3.371%   $168.0502   $168.05   $168.05   $168.10  
  Purchase #4 $119.73   10.624%   $132.4501   $132.45   $132.45   $132.50  
  Purchase #5 $83.50   13.686%   $94.9278   $94.93   $94.95   $94.90  
  Purchase #6 $203.71   9.587%   $223.2397   $223.24   $223.25   $223.20  
  Purchase #7 $249.89   6.688%   $266.6026   $266.60   $266.60   $266.60  
  7 purchase totals = $1,156.29       $1,262.0869   $1,262.09   $1,262.10   $1,262.10