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 $114.85   4.342%   $119.8368   $119.84   $119.85   $119.80  
  Purchase #2 $246.80   3.252%   $254.8259   $254.83   $254.85   $254.80  
  Purchase #3 $139.56   3.368%   $144.2604   $144.26   $144.25   $144.30  
  Purchase #4 $172.46   10.800%   $191.0857   $191.09   $191.10   $191.10  
  Purchase #5 $171.62   5.186%   $180.5202   $180.52   $180.50   $180.50  
  Purchase #6 $27.67   10.579%   $30.5972   $30.60   $30.60   $30.60  
  Purchase #7 $25.63   13.649%   $29.1282   $29.13   $29.15   $29.10  
  7 purchase totals = $898.59       $950.2544   $950.27   $950.30   $950.20