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 $64.74   13.725%   $73.6256   $73.63   $73.65   $73.60  
  Purchase #2 $228.58   5.523%   $241.2045   $241.20   $241.20   $241.20  
  Purchase #3 $17.90   10.226%   $19.7305   $19.73   $19.75   $19.70  
  Purchase #4 $88.47   11.759%   $98.8732   $98.87   $98.85   $98.90  
  Purchase #5 $246.72   12.672%   $277.9844   $277.98   $278.00   $278.00  
  Purchase #6 $214.74   4.683%   $224.7963   $224.80   $224.80   $224.80  
  Purchase #7 $193.32   9.287%   $211.2736   $211.27   $211.25   $211.30  
  7 purchase totals = $1,054.47       $1,147.4881   $1,147.48   $1,147.50   $1,147.50