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 $59.41   10.762%   $65.8037   $65.80   $65.80   $65.80  
  Purchase #2 $231.78   13.664%   $263.4504   $263.45   $263.45   $263.50  
  Purchase #3 $221.89   5.174%   $233.3706   $233.37   $233.35   $233.40  
  Purchase #4 $60.44   9.202%   $66.0017   $66.00   $66.00   $66.00  
  Purchase #5 $113.27   5.684%   $119.7083   $119.71   $119.70   $119.70  
  Purchase #6 $7.93   8.564%   $8.6091   $8.61   $8.60   $8.60  
  Purchase #7 $226.71   8.821%   $246.7081   $246.71   $246.70   $246.70  
  7 purchase totals = $921.43       $1,003.6519   $1,003.65   $1,003.60   $1,003.70