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 $51.99   10.486%   $57.4417   $57.44   $57.45   $57.40  
  Purchase #2 $143.78   13.336%   $162.9545   $162.95   $162.95   $163.00  
  Purchase #3 $74.31   8.695%   $80.7713   $80.77   $80.75   $80.80  
  Purchase #4 $205.51   13.575%   $233.408   $233.41   $233.40   $233.40  
  Purchase #5 $205.69   4.245%   $214.4215   $214.42   $214.40   $214.40  
  Purchase #6 $206.80   8.837%   $225.0749   $225.07   $225.05   $225.10  
  Purchase #7 $231.58   8.769%   $251.8873   $251.89   $251.90   $251.90  
  7 purchase totals = $1,119.66       $1,225.9592   $1,225.95   $1,225.90   $1,226.00