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 $208.27   12.246%   $233.7747   $233.77   $233.75   $233.80  
  Purchase #2 $121.50   3.491%   $125.7416   $125.74   $125.75   $125.70  
  Purchase #3 $160.95   11.543%   $179.5285   $179.53   $179.55   $179.50  
  Purchase #4 $155.83   13.842%   $177.4   $177.40   $177.40   $177.40  
  Purchase #5 $245.58   12.643%   $276.6287   $276.63   $276.65   $276.60  
  Purchase #6 $110.28   11.857%   $123.3559   $123.36   $123.35   $123.40  
  Purchase #7 $120.74   11.252%   $134.3257   $134.33   $134.35   $134.30  
  7 purchase totals = $1,123.15       $1,250.7551   $1,250.76   $1,250.80   $1,250.70