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 $208.98   11.446%   $232.8999   $232.90   $232.90   $232.90  
  Purchase #2 $70.91   6.631%   $75.612   $75.61   $75.60   $75.60  
  Purchase #3 $26.93   5.169%   $28.322   $28.32   $28.30   $28.30  
  Purchase #4 $204.46   9.203%   $223.2765   $223.28   $223.30   $223.30  
  Purchase #5 $106.86   8.479%   $115.9207   $115.92   $115.90   $115.90  
  Purchase #6 $14.30   7.476%   $15.3691   $15.37   $15.35   $15.40  
  Purchase #7 $63.25   3.680%   $65.5776   $65.58   $65.60   $65.60  
  7 purchase totals = $695.69       $756.9778   $756.98   $756.95   $757.00