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 $208.87   4.858%   $219.0169   $219.02   $219.00   $219.00  
  Purchase #2 $94.74   8.219%   $102.5267   $102.53   $102.55   $102.50  
  Purchase #3 $60.32   10.308%   $66.5378   $66.54   $66.55   $66.50  
  Purchase #4 $9.98   13.219%   $11.2993   $11.30   $11.30   $11.30  
  Purchase #5 $137.29   7.274%   $147.2765   $147.28   $147.30   $147.30  
  Purchase #6 $237.80   9.620%   $260.6764   $260.68   $260.70   $260.70  
  Purchase #7 $6.95   6.536%   $7.4043   $7.40   $7.40   $7.40  
  7 purchase totals = $755.95       $814.7379   $814.75   $814.80   $814.70