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 $115.84   9.416%   $126.7475   $126.75   $126.75   $126.70  
  Purchase #2 $175.71   4.238%   $183.1566   $183.16   $183.15   $183.20  
  Purchase #3 $226.84   11.367%   $252.6249   $252.62   $252.60   $252.60  
  Purchase #4 $59.57   12.401%   $66.9573   $66.96   $66.95   $67.00  
  Purchase #5 $14.58   7.527%   $15.6774   $15.68   $15.70   $15.70  
  Purchase #6 $18.27   6.812%   $19.5146   $19.51   $19.50   $19.50  
  Purchase #7 $231.54   4.152%   $241.1535   $241.15   $241.15   $241.20  
  7 purchase totals = $842.35       $905.8318   $905.83   $905.80   $905.90