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 $97.57   11.534%   $108.8237   $108.82   $108.80   $108.80  
  Purchase #2 $213.47   11.319%   $237.6327   $237.63   $237.65   $237.60  
  Purchase #3 $23.87   11.638%   $26.648   $26.65   $26.65   $26.60  
  Purchase #4 $234.81   6.161%   $249.2766   $249.28   $249.30   $249.30  
  Purchase #5 $27.68   12.844%   $31.2352   $31.24   $31.25   $31.20  
  Purchase #6 $163.85   10.420%   $180.9232   $180.92   $180.90   $180.90  
  Purchase #7 $204.71   13.736%   $232.829   $232.83   $232.85   $232.80  
  7 purchase totals = $965.96       $1,067.3684   $1,067.37   $1,067.40   $1,067.20