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 $151.77   8.179%   $164.1833   $164.18   $164.20   $164.20  
  Purchase #2 $24.69   8.370%   $26.7566   $26.76   $26.75   $26.80  
  Purchase #3 $232.76   7.824%   $250.9711   $250.97   $250.95   $251.00  
  Purchase #4 $117.41   7.286%   $125.9645   $125.96   $125.95   $126.00  
  Purchase #5 $44.56   7.769%   $48.0219   $48.02   $48.00   $48.00  
  Purchase #6 $200.38   7.468%   $215.3444   $215.34   $215.35   $215.30  
  Purchase #7 $24.86   10.728%   $27.527   $27.53   $27.55   $27.50  
  7 purchase totals = $796.43       $858.7688   $858.76   $858.75   $858.80