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 $65.68   11.122%   $72.9849   $72.98   $73.00   $73.00  
  Purchase #2 $163.28   3.300%   $168.6682   $168.67   $168.65   $168.70  
  Purchase #3 $124.47   9.634%   $136.4614   $136.46   $136.45   $136.50  
  Purchase #4 $247.45   3.799%   $256.8506   $256.85   $256.85   $256.90  
  Purchase #5 $216.53   6.806%   $231.267   $231.27   $231.25   $231.30  
  Purchase #6 $112.48   8.697%   $122.2624   $122.26   $122.25   $122.30  
  Purchase #7 $241.87   12.859%   $272.9721   $272.97   $272.95   $273.00  
  7 purchase totals = $1,171.76       $1,261.4666   $1,261.46   $1,261.40   $1,261.70