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 $198.63   7.242%   $213.0148   $213.01   $213.00   $213.00  
  Purchase #2 $52.91   6.137%   $56.1571   $56.16   $56.15   $56.20  
  Purchase #3 $139.30   12.538%   $156.7654   $156.77   $156.75   $156.80  
  Purchase #4 $189.97   8.531%   $206.1763   $206.18   $206.20   $206.20  
  Purchase #5 $226.41   10.494%   $250.1695   $250.17   $250.15   $250.20  
  Purchase #6 $127.84   4.516%   $133.6133   $133.61   $133.60   $133.60  
  Purchase #7 $235.48   3.693%   $244.1763   $244.18   $244.20   $244.20  
  7 purchase totals = $1,170.54       $1,260.0727   $1,260.08   $1,260.05   $1,260.20