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 $208.30   3.816%   $216.2487   $216.25   $216.25   $216.20  
  Purchase #2 $95.57   9.472%   $104.6224   $104.62   $104.60   $104.60  
  Purchase #3 $246.30   4.106%   $256.4131   $256.41   $256.40   $256.40  
  Purchase #4 $243.87   6.724%   $260.2678   $260.27   $260.25   $260.30  
  Purchase #5 $154.46   10.398%   $170.5208   $170.52   $170.50   $170.50  
  Purchase #6 $197.53   4.364%   $206.1502   $206.15   $206.15   $206.20  
  Purchase #7 $15.52   13.169%   $17.5638   $17.56   $17.55   $17.60  
  7 purchase totals = $1,161.55       $1,231.7868   $1,231.78   $1,231.70   $1,231.80