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 $196.59   3.719%   $203.9012   $203.90   $203.90   $203.90  
  Purchase #2 $215.63   10.828%   $238.9784   $238.98   $239.00   $239.00  
  Purchase #3 $143.35   13.866%   $163.2269   $163.23   $163.25   $163.20  
  Purchase #4 $148.49   3.801%   $154.1341   $154.13   $154.15   $154.10  
  Purchase #5 $26.90   3.142%   $27.7452   $27.75   $27.75   $27.70  
  Purchase #6 $179.76   13.713%   $204.4105   $204.41   $204.40   $204.40  
  Purchase #7 $79.93   5.716%   $84.4988   $84.50   $84.50   $84.50  
  7 purchase totals = $990.65       $1,076.8951   $1,076.90   $1,076.95   $1,076.80