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 $168.77   9.798%   $185.3061   $185.31   $185.30   $185.30  
  Purchase #2 $158.38   9.394%   $173.2582   $173.26   $173.25   $173.30  
  Purchase #3 $242.92   9.593%   $266.2233   $266.22   $266.20   $266.20  
  Purchase #4 $184.87   11.716%   $206.5294   $206.53   $206.55   $206.50  
  Purchase #5 $63.79   3.642%   $66.1132   $66.11   $66.10   $66.10  
  Purchase #6 $146.78   3.493%   $151.907   $151.91   $151.90   $151.90  
  Purchase #7 $175.70   6.535%   $187.182   $187.18   $187.20   $187.20  
  7 purchase totals = $1,141.21       $1,236.5192   $1,236.52   $1,236.50   $1,236.50