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	$36.42	10.293%	$40.1687	$40.17	$40.15	$40.20
Purchase #2	$35.52	7.223%	$38.0856	$38.09	$38.10	$38.10
Purchase #3	$65.95	10.287%	$72.7343	$72.73	$72.75	$72.70
Purchase #4	$174.41	8.251%	$188.8006	$188.80	$188.80	$188.80
Purchase #5	$99.27	13.752%	$112.9216	$112.92	$112.90	$112.90
Purchase #6	$196.32	4.280%	$204.7225	$204.72	$204.70	$204.70
Purchase #7	$88.35	13.157%	$99.9742	$99.97	$99.95	$100.00
7 purchase totals =	$696.24		$757.4075	$757.40	$757.35	$757.40