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 $202.91   6.106%   $215.2997   $215.30   $215.30   $215.30  
  Purchase #2 $191.61   8.351%   $207.6114   $207.61   $207.60   $207.60  
  Purchase #3 $88.46   5.357%   $93.1988   $93.20   $93.20   $93.20  
  Purchase #4 $62.42   11.600%   $69.6607   $69.66   $69.65   $69.70  
  Purchase #5 $79.90   3.454%   $82.6597   $82.66   $82.65   $82.70  
  Purchase #6 $60.81   4.155%   $63.3367   $63.34   $63.35   $63.30  
  Purchase #7 $150.67   6.183%   $159.9859   $159.99   $160.00   $160.00  
  7 purchase totals = $836.78       $891.7529   $891.76   $891.75   $891.80