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 $134.62   13.795%   $153.1908   $153.19   $153.20   $153.20  
  Purchase #2 $138.74   10.467%   $153.2619   $153.26   $153.25   $153.30  
  Purchase #3 $113.36   9.835%   $124.509   $124.51   $124.50   $124.50  
  Purchase #4 $22.70   11.632%   $25.3405   $25.34   $25.35   $25.30  
  Purchase #5 $112.76   11.210%   $125.4004   $125.40   $125.40   $125.40  
  Purchase #6 $249.53   11.765%   $278.8872   $278.89   $278.90   $278.90  
  Purchase #7 $187.69   3.576%   $194.4018   $194.40   $194.40   $194.40  
  7 purchase totals = $959.40       $1,054.9916   $1,054.99   $1,055.00   $1,055.00