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 $61.76   8.791%   $67.1893   $67.19   $67.20   $67.20  
  Purchase #2 $61.28   3.636%   $63.5081   $63.51   $63.50   $63.50  
  Purchase #3 $91.37   7.633%   $98.3443   $98.34   $98.35   $98.30  
  Purchase #4 $52.41   9.517%   $57.3979   $57.40   $57.40   $57.40  
  Purchase #5 $246.86   5.427%   $260.2571   $260.26   $260.25   $260.30  
  Purchase #6 $122.88   9.322%   $134.3349   $134.33   $134.35   $134.30  
  Purchase #7 $52.86   7.737%   $56.9498   $56.95   $56.95   $56.90  
  7 purchase totals = $689.42       $737.9814   $737.98   $738.00   $737.90