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 $19.76   5.197%   $20.7869   $20.79   $20.80   $20.80  
  Purchase #2 $99.71   7.846%   $107.5332   $107.53   $107.55   $107.50  
  Purchase #3 $97.82   11.297%   $108.8707   $108.87   $108.85   $108.90  
  Purchase #4 $246.75   10.499%   $272.6563   $272.66   $272.65   $272.70  
  Purchase #5 $183.36   3.566%   $189.8986   $189.90   $189.90   $189.90  
  Purchase #6 $107.85   3.493%   $111.6172   $111.62   $111.60   $111.60  
  Purchase #7 $116.74   7.416%   $125.3974   $125.40   $125.40   $125.40  
  7 purchase totals = $871.99       $936.7603   $936.77   $936.75   $936.80