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 $72.54   5.512%   $76.5384   $76.54   $76.55   $76.50  
  Purchase #2 $196.42   7.716%   $211.5758   $211.58   $211.60   $211.60  
  Purchase #3 $246.49   10.711%   $272.8915   $272.89   $272.90   $272.90  
  Purchase #4 $51.50   9.514%   $56.3997   $56.40   $56.40   $56.40  
  Purchase #5 $98.65   8.694%   $107.2266   $107.23   $107.25   $107.20  
  Purchase #6 $195.89   11.323%   $218.0706   $218.07   $218.05   $218.10  
  Purchase #7 $55.28   10.296%   $60.9716   $60.97   $60.95   $61.00  
  7 purchase totals = $916.77       $1,003.6742   $1,003.68   $1,003.70   $1,003.70