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 $194.55   6.381%   $206.9642   $206.96   $206.95   $207.00  
  Purchase #2 $207.60   4.597%   $217.1434   $217.14   $217.15   $217.10  
  Purchase #3 $10.39   13.210%   $11.7625   $11.76   $11.75   $11.80  
  Purchase #4 $95.35   10.200%   $105.0757   $105.08   $105.10   $105.10  
  Purchase #5 $164.35   10.851%   $182.1836   $182.18   $182.20   $182.20  
  Purchase #6 $219.71   5.811%   $232.4773   $232.48   $232.50   $232.50  
  Purchase #7 $105.85   7.597%   $113.8914   $113.89   $113.90   $113.90  
  7 purchase totals = $997.80       $1,069.4981   $1,069.49   $1,069.55   $1,069.60