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	$64.92	8.818%	$70.6446	$70.64	$70.65	$70.60
Purchase #2	$99.98	5.420%	$105.3989	$105.40	$105.40	$105.40
Purchase #3	$39.46	12.281%	$44.3061	$44.31	$44.30	$44.30
Purchase #4	$231.53	4.581%	$242.1364	$242.14	$242.15	$242.10
Purchase #5	$150.35	3.427%	$155.5025	$155.50	$155.50	$155.50
Purchase #6	$90.77	10.817%	$100.5886	$100.59	$100.60	$100.60
Purchase #7	$64.91	9.522%	$71.0907	$71.09	$71.10	$71.10
7 purchase totals =	$741.92		$789.6678	$789.67	$789.70	$789.60