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	$70.46	13.677%	$80.0968	$80.10	$80.10	$80.10
Purchase #2	$66.52	6.787%	$71.0347	$71.03	$71.05	$71.00
Purchase #3	$51.42	5.728%	$54.3653	$54.37	$54.35	$54.40
Purchase #4	$112.72	4.552%	$117.851	$117.85	$117.85	$117.90
Purchase #5	$110.36	11.584%	$123.1441	$123.14	$123.15	$123.10
Purchase #6	$162.41	6.129%	$172.3641	$172.36	$172.35	$172.40
Purchase #7	$170.35	3.814%	$176.8471	$176.85	$176.85	$176.80
7 purchase totals =	$744.24		$795.7031	$795.70	$795.70	$795.70