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 $239.71   11.363%   $266.9482   $266.95   $266.95   $266.90  
  Purchase #2 $29.86   7.718%   $32.1646   $32.16   $32.15   $32.20  
  Purchase #3 $96.62   10.484%   $106.7496   $106.75   $106.75   $106.70  
  Purchase #4 $205.93   5.756%   $217.7833   $217.78   $217.80   $217.80  
  Purchase #5 $148.78   12.383%   $167.2034   $167.20   $167.20   $167.20  
  Purchase #6 $196.54   7.657%   $211.5891   $211.59   $211.60   $211.60  
  Purchase #7 $46.93   13.475%   $53.2538   $53.25   $53.25   $53.30  
  7 purchase totals = $964.37       $1,055.6920   $1,055.68   $1,055.70   $1,055.70