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 $32.50   4.818%   $34.0659   $34.07   $34.05   $34.10  
  Purchase #2 $122.69   5.863%   $129.8833   $129.88   $129.90   $129.90  
  Purchase #3 $87.56   8.617%   $95.105   $95.11   $95.10   $95.10  
  Purchase #4 $191.39   6.654%   $204.1251   $204.13   $204.15   $204.10  
  Purchase #5 $69.25   6.505%   $73.7547   $73.75   $73.75   $73.80  
  Purchase #6 $164.60   13.710%   $187.1667   $187.17   $187.15   $187.20  
  Purchase #7 $236.62   7.606%   $254.6173   $254.62   $254.60   $254.60  
  7 purchase totals = $904.61       $978.7180   $978.73   $978.70   $978.80