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 $216.46   13.521%   $245.7276   $245.73   $245.75   $245.70  
  Purchase #2 $212.93   10.321%   $234.9065   $234.91   $234.90   $234.90  
  Purchase #3 $60.29   4.703%   $63.1254   $63.13   $63.15   $63.10  
  Purchase #4 $41.99   6.361%   $44.661   $44.66   $44.65   $44.70  
  Purchase #5 $66.34   5.389%   $69.9151   $69.92   $69.90   $69.90  
  Purchase #6 $201.99   8.864%   $219.8944   $219.89   $219.90   $219.90  
  Purchase #7 $27.39   9.534%   $30.0014   $30.00   $30.00   $30.00  
  7 purchase totals = $827.39       $908.2314   $908.24   $908.25   $908.20