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 $86.87   10.165%   $95.7003   $95.70   $95.70   $95.70  
  Purchase #2 $200.50   7.259%   $215.0543   $215.05   $215.05   $215.10  
  Purchase #3 $178.74   12.827%   $201.667   $201.67   $201.65   $201.70  
  Purchase #4 $12.69   10.328%   $14.0006   $14.00   $14.00   $14.00  
  Purchase #5 $80.55   4.374%   $84.0733   $84.07   $84.05   $84.10  
  Purchase #6 $201.48   5.167%   $211.8905   $211.89   $211.90   $211.90  
  Purchase #7 $163.58   8.423%   $177.3583   $177.36   $177.35   $177.40  
  7 purchase totals = $924.41       $999.7443   $999.74   $999.70   $999.90