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 $250.41   6.653%   $267.0698   $267.07   $267.05   $267.10  
  Purchase #2 $48.88   5.339%   $51.4897   $51.49   $51.50   $51.50  
  Purchase #3 $247.59   8.735%   $269.217   $269.22   $269.20   $269.20  
  Purchase #4 $240.57   11.438%   $268.0864   $268.09   $268.10   $268.10  
  Purchase #5 $226.49   8.405%   $245.5265   $245.53   $245.55   $245.50  
  Purchase #6 $162.41   6.873%   $173.5724   $173.57   $173.55   $173.60  
  Purchase #7 $52.86   3.496%   $54.708   $54.71   $54.70   $54.70  
  7 purchase totals = $1,229.21       $1,329.6698   $1,329.68   $1,329.65   $1,329.70