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 $61.55   3.841%   $63.9141   $63.91   $63.90   $63.90  
  Purchase #2 $187.85   11.238%   $208.9606   $208.96   $208.95   $209.00  
  Purchase #3 $159.99   8.358%   $173.362   $173.36   $173.35   $173.40  
  Purchase #4 $94.74   12.376%   $106.465   $106.47   $106.45   $106.50  
  Purchase #5 $83.88   12.597%   $94.4464   $94.45   $94.45   $94.40  
  Purchase #6 $62.71   5.300%   $66.0336   $66.03   $66.05   $66.00  
  Purchase #7 $74.54   6.216%   $79.1734   $79.17   $79.15   $79.20  
  7 purchase totals = $725.26       $792.3551   $792.35   $792.30   $792.40