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 $250.27   5.716%   $264.5754   $264.58   $264.60   $264.60  
  Purchase #2 $227.70   13.245%   $257.8589   $257.86   $257.85   $257.90  
  Purchase #3 $209.30   10.670%   $231.6323   $231.63   $231.65   $231.60  
  Purchase #4 $95.31   3.699%   $98.8355   $98.84   $98.85   $98.80  
  Purchase #5 $213.39   13.293%   $241.7559   $241.76   $241.75   $241.80  
  Purchase #6 $162.60   13.139%   $183.964   $183.96   $183.95   $184.00  
  Purchase #7 $171.28   5.256%   $180.2825   $180.28   $180.30   $180.30  
  7 purchase totals = $1,329.85       $1,458.9045   $1,458.91   $1,458.95   $1,459.00