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 $156.73   3.388%   $162.04   $162.04   $162.05   $162.00  
  Purchase #2 $226.27   6.480%   $240.9323   $240.93   $240.95   $240.90  
  Purchase #3 $23.67   6.325%   $25.1671   $25.17   $25.15   $25.20  
  Purchase #4 $67.76   3.838%   $70.3606   $70.36   $70.35   $70.40  
  Purchase #5 $93.85   12.235%   $105.3325   $105.33   $105.35   $105.30  
  Purchase #6 $222.44   12.140%   $249.4442   $249.44   $249.45   $249.40  
  Purchase #7 $74.37   9.797%   $81.656   $81.66   $81.65   $81.70  
  7 purchase totals = $865.09       $934.9327   $934.93   $934.95   $934.90