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 $185.68   11.486%   $207.0072   $207.01   $207.00   $207.00  
  Purchase #2 $124.59   11.874%   $139.3838   $139.38   $139.40   $139.40  
  Purchase #3 $236.53   5.435%   $249.3854   $249.39   $249.40   $249.40  
  Purchase #4 $75.39   9.405%   $82.4804   $82.48   $82.50   $82.50  
  Purchase #5 $181.73   11.631%   $202.867   $202.87   $202.85   $202.90  
  Purchase #6 $26.28   3.208%   $27.1231   $27.12   $27.10   $27.10  
  Purchase #7 $163.82   9.716%   $179.7368   $179.74   $179.75   $179.70  
  7 purchase totals = $994.02       $1,087.9837   $1,087.99   $1,088.00   $1,088.00