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 $51.25   6.558%   $54.611   $54.61   $54.60   $54.60  
  Purchase #2 $171.51   5.719%   $181.3187   $181.32   $181.30   $181.30  
  Purchase #3 $26.99   6.703%   $28.7991   $28.80   $28.80   $28.80  
  Purchase #4 $208.43   3.157%   $215.0101   $215.01   $215.00   $215.00  
  Purchase #5 $53.65   10.247%   $59.1475   $59.15   $59.15   $59.10  
  Purchase #6 $170.69   10.723%   $188.9931   $188.99   $189.00   $189.00  
  Purchase #7 $73.47   6.374%   $78.153   $78.15   $78.15   $78.20  
  7 purchase totals = $755.99       $806.0325   $806.03   $806.00   $806.00