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 $208.90   11.631%   $233.1972   $233.20   $233.20   $233.20  
  Purchase #2 $44.58   9.541%   $48.8334   $48.83   $48.85   $48.80  
  Purchase #3 $64.89   6.834%   $69.3246   $69.32   $69.30   $69.30  
  Purchase #4 $51.53   7.128%   $55.2031   $55.20   $55.20   $55.20  
  Purchase #5 $112.80   10.199%   $124.3045   $124.30   $124.30   $124.30  
  Purchase #6 $198.70   7.553%   $213.7078   $213.71   $213.70   $213.70  
  Purchase #7 $247.54   11.632%   $276.3339   $276.33   $276.35   $276.30  
  7 purchase totals = $928.94       $1,020.9045   $1,020.89   $1,020.90   $1,020.80