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 $186.67   3.402%   $193.0205   $193.02   $193.00   $193.00  
  Purchase #2 $180.42   11.797%   $201.7041   $201.70   $201.70   $201.70  
  Purchase #3 $123.90   10.766%   $137.2391   $137.24   $137.25   $137.20  
  Purchase #4 $146.64   10.861%   $162.5666   $162.57   $162.55   $162.60  
  Purchase #5 $59.96   11.772%   $67.0185   $67.02   $67.00   $67.00  
  Purchase #6 $230.96   9.783%   $253.5548   $253.55   $253.55   $253.60  
  Purchase #7 $146.53   11.689%   $163.6579   $163.66   $163.65   $163.70  
  7 purchase totals = $1,075.08       $1,178.7615   $1,178.76   $1,178.70   $1,178.80