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 $181.35   7.262%   $194.5196   $194.52   $194.50   $194.50  
  Purchase #2 $249.78   4.778%   $261.7145   $261.71   $261.70   $261.70  
  Purchase #3 $148.58   9.430%   $162.5911   $162.59   $162.60   $162.60  
  Purchase #4 $175.32   10.825%   $194.2984   $194.30   $194.30   $194.30  
  Purchase #5 $115.77   13.326%   $131.1975   $131.20   $131.20   $131.20  
  Purchase #6 $104.74   10.460%   $115.6958   $115.70   $115.70   $115.70  
  Purchase #7 $173.90   6.409%   $185.0453   $185.05   $185.05   $185.00  
  7 purchase totals = $1,149.44       $1,245.0622   $1,245.07   $1,245.05   $1,245.00