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 $134.33   10.632%   $148.612   $148.61   $148.60   $148.60  
  Purchase #2 $244.91   4.474%   $255.8673   $255.87   $255.85   $255.90  
  Purchase #3 $103.32   4.759%   $108.237   $108.24   $108.25   $108.20  
  Purchase #4 $95.72   5.807%   $101.2785   $101.28   $101.30   $101.30  
  Purchase #5 $14.96   10.374%   $16.512   $16.51   $16.50   $16.50  
  Purchase #6 $63.66   8.144%   $68.8445   $68.84   $68.85   $68.80  
  Purchase #7 $22.46   3.569%   $23.2616   $23.26   $23.25   $23.30  
  7 purchase totals = $679.36       $722.6129   $722.61   $722.60   $722.60