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 $59.58   6.469%   $63.4342   $63.43   $63.45   $63.40  
  Purchase #2 $196.39   9.379%   $214.8094   $214.81   $214.80   $214.80  
  Purchase #3 $223.94   12.475%   $251.8765   $251.88   $251.90   $251.90  
  Purchase #4 $242.93   6.189%   $257.9649   $257.96   $257.95   $258.00  
  Purchase #5 $152.56   6.330%   $162.217   $162.22   $162.20   $162.20  
  Purchase #6 $128.41   5.679%   $135.7024   $135.70   $135.70   $135.70  
  Purchase #7 $53.85   13.325%   $61.0255   $61.03   $61.05   $61.00  
  7 purchase totals = $1,057.66       $1,147.0299   $1,147.03   $1,147.05   $1,147.00