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 $244.78   6.274%   $260.1375   $260.14   $260.15   $260.10  
  Purchase #2 $207.28   3.332%   $214.1866   $214.19   $214.20   $214.20  
  Purchase #3 $98.42   3.527%   $101.8913   $101.89   $101.90   $101.90  
  Purchase #4 $61.73   8.350%   $66.8845   $66.88   $66.90   $66.90  
  Purchase #5 $198.84   4.128%   $207.0481   $207.05   $207.05   $207.00  
  Purchase #6 $155.65   7.452%   $167.249   $167.25   $167.25   $167.20  
  Purchase #7 $15.50   13.349%   $17.5691   $17.57   $17.55   $17.60  
  7 purchase totals = $982.20       $1,034.9661   $1,034.97   $1,035.00   $1,034.90