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 $248.42   7.280%   $266.505   $266.51   $266.50   $266.50  
  Purchase #2 $105.88   10.689%   $117.1975   $117.20   $117.20   $117.20  
  Purchase #3 $15.66   10.419%   $17.2916   $17.29   $17.30   $17.30  
  Purchase #4 $159.48   11.351%   $177.5826   $177.58   $177.60   $177.60  
  Purchase #5 $188.60   6.262%   $200.4101   $200.41   $200.40   $200.40  
  Purchase #6 $112.29   12.367%   $126.1769   $126.18   $126.20   $126.20  
  Purchase #7 $157.97   6.279%   $167.8889   $167.89   $167.90   $167.90  
  7 purchase totals = $988.30       $1,073.0526   $1,073.06   $1,073.10   $1,073.10