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 $59.62   13.840%   $67.8714   $67.87   $67.85   $67.90  
  Purchase #2 $92.85   9.756%   $101.9084   $101.91   $101.90   $101.90  
  Purchase #3 $49.59   8.306%   $53.7089   $53.71   $53.70   $53.70  
  Purchase #4 $244.96   8.614%   $266.0609   $266.06   $266.05   $266.10  
  Purchase #5 $94.69   5.278%   $99.6877   $99.69   $99.70   $99.70  
  Purchase #6 $46.60   5.564%   $49.1928   $49.19   $49.20   $49.20  
  Purchase #7 $174.88   11.247%   $194.5488   $194.55   $194.55   $194.50  
  7 purchase totals = $763.19       $832.9789   $832.98   $832.95   $833.00