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 $198.89   13.627%   $225.9927   $225.99   $226.00   $226.00  
  Purchase #2 $206.31   13.437%   $234.0319   $234.03   $234.05   $234.00  
  Purchase #3 $225.64   8.622%   $245.0947   $245.09   $245.10   $245.10  
  Purchase #4 $145.65   9.311%   $159.2115   $159.21   $159.20   $159.20  
  Purchase #5 $152.41   7.766%   $164.2462   $164.25   $164.25   $164.20  
  Purchase #6 $10.93   7.781%   $11.7805   $11.78   $11.80   $11.80  
  Purchase #7 $125.80   9.336%   $137.5447   $137.54   $137.55   $137.50  
  7 purchase totals = $1,065.63       $1,177.9022   $1,177.89   $1,177.95   $1,177.80