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 $93.33   12.544%   $105.0373   $105.04   $105.05   $105.00  
  Purchase #2 $19.82   7.118%   $21.2308   $21.23   $21.25   $21.20  
  Purchase #3 $46.36   5.680%   $48.9932   $48.99   $49.00   $49.00  
  Purchase #4 $159.85   3.564%   $165.5471   $165.55   $165.55   $165.50  
  Purchase #5 $185.42   12.701%   $208.9702   $208.97   $208.95   $209.00  
  Purchase #6 $166.97   13.745%   $189.92   $189.92   $189.90   $189.90  
  Purchase #7 $174.87   7.702%   $188.3385   $188.34   $188.35   $188.30  
  7 purchase totals = $846.62       $928.0371   $928.04   $928.05   $927.90