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	$40.77	4.321%	$42.5317	$42.53	$42.55	$42.50
Purchase #2	$134.66	12.712%	$151.778	$151.78	$151.80	$151.80
Purchase #3	$61.50	5.450%	$64.8518	$64.85	$64.85	$64.90
Purchase #4	$111.59	3.448%	$115.4376	$115.44	$115.45	$115.40
Purchase #5	$218.37	9.179%	$238.4142	$238.41	$238.40	$238.40
Purchase #6	$205.29	12.454%	$230.8568	$230.86	$230.85	$230.90
Purchase #7	$228.55	10.843%	$253.3317	$253.33	$253.35	$253.30
7 purchase totals =	$1,000.73		$1,097.2018	$1,097.20	$1,097.25	$1,097.20