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 $246.91   11.219%   $274.6108   $274.61   $274.60   $274.60  
  Purchase #2 $38.72   4.253%   $40.3668   $40.37   $40.35   $40.40  
  Purchase #3 $218.98   11.276%   $243.6722   $243.67   $243.65   $243.70  
  Purchase #4 $77.97   4.107%   $81.1722   $81.17   $81.15   $81.20  
  Purchase #5 $69.83   10.723%   $77.3179   $77.32   $77.30   $77.30  
  Purchase #6 $6.76   4.620%   $7.0723   $7.07   $7.05   $7.10  
  Purchase #7 $34.90   3.535%   $36.1337   $36.13   $36.15   $36.10  
  7 purchase totals = $694.07       $760.3459   $760.34   $760.25   $760.40