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 $168.81   10.635%   $186.7629   $186.76   $186.75   $186.80  
  Purchase #2 $205.39   6.670%   $219.0895   $219.09   $219.10   $219.10  
  Purchase #3 $162.68   5.605%   $171.7982   $171.80   $171.80   $171.80  
  Purchase #4 $211.82   5.833%   $224.1755   $224.18   $224.20   $224.20  
  Purchase #5 $50.63   11.683%   $56.5451   $56.55   $56.55   $56.50  
  Purchase #6 $242.64   13.187%   $274.6369   $274.64   $274.65   $274.60  
  Purchase #7 $184.43   13.863%   $209.9975   $210.00   $210.00   $210.00  
  7 purchase totals = $1,226.40       $1,343.0056   $1,343.02   $1,343.05   $1,343.00