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 $194.93   6.673%   $207.9377   $207.94   $207.95   $207.90  
  Purchase #2 $145.80   4.181%   $151.8959   $151.90   $151.90   $151.90  
  Purchase #3 $123.65   9.124%   $134.9318   $134.93   $134.95   $134.90  
  Purchase #4 $218.43   9.549%   $239.2879   $239.29   $239.30   $239.30  
  Purchase #5 $145.93   9.606%   $159.948   $159.95   $159.95   $159.90  
  Purchase #6 $240.82   13.789%   $274.0267   $274.03   $274.05   $274.00  
  Purchase #7 $98.71   6.533%   $105.1587   $105.16   $105.15   $105.20  
  7 purchase totals = $1,168.27       $1,273.1867   $1,273.20   $1,273.25   $1,273.10