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 $184.42   6.193%   $195.8411   $195.84   $195.85   $195.80  
  Purchase #2 $112.80   10.455%   $124.5932   $124.59   $124.60   $124.60  
  Purchase #3 $122.49   5.468%   $129.1878   $129.19   $129.20   $129.20  
  Purchase #4 $67.83   8.507%   $73.6003   $73.60   $73.60   $73.60  
  Purchase #5 $111.84   6.503%   $119.113   $119.11   $119.10   $119.10  
  Purchase #6 $139.35   6.397%   $148.2642   $148.26   $148.25   $148.30  
  Purchase #7 $246.93   9.266%   $269.8105   $269.81   $269.80   $269.80  
  7 purchase totals = $985.66       $1,060.4101   $1,060.40   $1,060.40   $1,060.40