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 $85.96   10.259%   $94.7786   $94.78   $94.80   $94.80  
  Purchase #2 $26.99   13.726%   $30.6946   $30.69   $30.70   $30.70  
  Purchase #3 $146.90   3.807%   $152.4925   $152.49   $152.50   $152.50  
  Purchase #4 $224.99   3.548%   $232.9726   $232.97   $232.95   $233.00  
  Purchase #5 $132.59   10.272%   $146.2096   $146.21   $146.20   $146.20  
  Purchase #6 $152.55   13.215%   $172.7095   $172.71   $172.70   $172.70  
  Purchase #7 $151.33   7.748%   $163.055   $163.06   $163.05   $163.10  
  7 purchase totals = $921.31       $992.9124   $992.91   $992.90   $993.00