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 $105.71   12.826%   $119.2684   $119.27   $119.25   $119.30  
  Purchase #2 $203.70   6.527%   $216.9955   $217.00   $217.00   $217.00  
  Purchase #3 $13.70   13.373%   $15.5321   $15.53   $15.55   $15.50  
  Purchase #4 $98.77   6.759%   $105.4459   $105.45   $105.45   $105.40  
  Purchase #5 $43.67   7.202%   $46.8151   $46.82   $46.80   $46.80  
  Purchase #6 $182.71   12.144%   $204.8983   $204.90   $204.90   $204.90  
  Purchase #7 $178.56   11.160%   $198.4873   $198.49   $198.50   $198.50  
  7 purchase totals = $826.82       $907.4426   $907.46   $907.45   $907.40