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 $92.48   6.438%   $98.4339   $98.43   $98.45   $98.40  
  Purchase #2 $124.63   12.434%   $140.1265   $140.13   $140.15   $140.10  
  Purchase #3 $166.81   4.261%   $173.9178   $173.92   $173.90   $173.90  
  Purchase #4 $102.98   10.403%   $113.693   $113.69   $113.70   $113.70  
  Purchase #5 $63.57   3.341%   $65.6939   $65.69   $65.70   $65.70  
  Purchase #6 $132.50   11.805%   $148.1416   $148.14   $148.15   $148.10  
  Purchase #7 $52.40   5.841%   $55.4607   $55.46   $55.45   $55.50  
  7 purchase totals = $735.37       $795.4674   $795.46   $795.50   $795.40