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 $87.47   12.535%   $98.4344   $98.43   $98.45   $98.40  
  Purchase #2 $191.54   3.814%   $198.8453   $198.85   $198.85   $198.80  
  Purchase #3 $104.74   13.625%   $119.0108   $119.01   $119.00   $119.00  
  Purchase #4 $233.37   4.240%   $243.2649   $243.26   $243.25   $243.30  
  Purchase #5 $236.86   5.334%   $249.4941   $249.49   $249.50   $249.50  
  Purchase #6 $148.48   5.659%   $156.8825   $156.88   $156.90   $156.90  
  Purchase #7 $155.35   11.526%   $173.2556   $173.26   $173.25   $173.30  
  7 purchase totals = $1,157.81       $1,239.1876   $1,239.18   $1,239.20   $1,239.20