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 $78.57   5.544%   $82.9259   $82.93   $82.95   $82.90  
  Purchase #2 $250.54   11.593%   $279.5851   $279.59   $279.60   $279.60  
  Purchase #3 $86.58   6.721%   $92.399   $92.40   $92.40   $92.40  
  Purchase #4 $249.59   6.456%   $265.7035   $265.70   $265.70   $265.70  
  Purchase #5 $186.91   10.482%   $206.5019   $206.50   $206.50   $206.50  
  Purchase #6 $46.64   4.662%   $48.8144   $48.81   $48.80   $48.80  
  Purchase #7 $203.41   13.684%   $231.2446   $231.24   $231.25   $231.20  
  7 purchase totals = $1,102.24       $1,207.1744   $1,207.17   $1,207.20   $1,207.10