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 $77.95   3.408%   $80.6065   $80.61   $80.60   $80.60  
  Purchase #2 $21.91   12.323%   $24.61   $24.61   $24.60   $24.60  
  Purchase #3 $242.60   5.421%   $255.7513   $255.75   $255.75   $255.80  
  Purchase #4 $86.69   11.541%   $96.6949   $96.69   $96.70   $96.70  
  Purchase #5 $53.27   9.859%   $58.5219   $58.52   $58.50   $58.50  
  Purchase #6 $167.26   9.826%   $183.695   $183.70   $183.70   $183.70  
  Purchase #7 $230.88   5.853%   $244.3934   $244.39   $244.40   $244.40  
  7 purchase totals = $880.56       $944.2730   $944.27   $944.25   $944.30