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	$138.63	7.133%	$148.5185	$148.52	$148.50	$148.50
Purchase #2	$32.33	6.332%	$34.3771	$34.38	$34.40	$34.40
Purchase #3	$28.79	11.616%	$32.1342	$32.13	$32.15	$32.10
Purchase #4	$147.57	12.223%	$165.6075	$165.61	$165.60	$165.60
Purchase #5	$141.72	10.228%	$156.2151	$156.22	$156.20	$156.20
Purchase #6	$43.38	6.646%	$46.263	$46.26	$46.25	$46.30
Purchase #7	$89.83	3.639%	$93.0989	$93.10	$93.10	$93.10
7 purchase totals =	$622.25		$676.2143	$676.22	$676.20	$676.20