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	$76.61	5.542%	$80.8557	$80.86	$80.85	$80.90
Purchase #2	$242.69	12.477%	$272.9704	$272.97	$272.95	$273.00
Purchase #3	$166.52	10.216%	$183.5317	$183.53	$183.55	$183.50
Purchase #4	$91.44	5.355%	$96.3366	$96.34	$96.35	$96.30
Purchase #5	$195.90	13.651%	$222.6423	$222.64	$222.65	$222.60
Purchase #6	$190.33	4.233%	$198.3867	$198.39	$198.40	$198.40
Purchase #7	$51.86	6.168%	$55.0587	$55.06	$55.05	$55.10
7 purchase totals =	$1,015.35		$1,109.7821	$1,109.79	$1,109.80	$1,109.80