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 $56.66   6.344%   $60.2545   $60.25   $60.25   $60.30  
  Purchase #2 $247.87   7.715%   $266.9932   $266.99   $267.00   $267.00  
  Purchase #3 $219.31   8.786%   $238.5786   $238.58   $238.60   $238.60  
  Purchase #4 $166.48   12.670%   $187.573   $187.57   $187.55   $187.60  
  Purchase #5 $15.81   5.590%   $16.6938   $16.69   $16.70   $16.70  
  Purchase #6 $240.49   3.240%   $248.2819   $248.28   $248.30   $248.30  
  Purchase #7 $66.60   13.806%   $75.7948   $75.79   $75.80   $75.80  
  7 purchase totals = $1,013.22       $1,094.1698   $1,094.15   $1,094.20   $1,094.30