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	$127.88	7.225%	$137.1193	$137.12	$137.10	$137.10
Purchase #2	$216.34	4.269%	$225.5756	$225.58	$225.60	$225.60
Purchase #3	$50.35	10.477%	$55.6252	$55.63	$55.65	$55.60
Purchase #4	$238.62	5.459%	$251.6463	$251.65	$251.65	$251.60
Purchase #5	$71.69	9.574%	$78.5536	$78.55	$78.55	$78.60
Purchase #6	$27.26	6.267%	$28.9684	$28.97	$28.95	$29.00
Purchase #7	$78.46	3.172%	$80.9488	$80.95	$80.95	$80.90
7 purchase totals =	$810.60		$858.4372	$858.45	$858.45	$858.40