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 $241.46   9.830%   $265.1955   $265.20   $265.20   $265.20  
  Purchase #2 $154.43   4.848%   $161.9168   $161.92   $161.90   $161.90  
  Purchase #3 $117.80   4.670%   $123.3013   $123.30   $123.30   $123.30  
  Purchase #4 $221.57   6.480%   $235.9277   $235.93   $235.95   $235.90  
  Purchase #5 $34.80   8.453%   $37.7416   $37.74   $37.75   $37.70  
  Purchase #6 $185.37   6.808%   $197.99   $197.99   $198.00   $198.00  
  Purchase #7 $64.50   10.518%   $71.2841   $71.28   $71.30   $71.30  
  7 purchase totals = $1,019.93       $1,093.3570   $1,093.36   $1,093.40   $1,093.30