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	$9.93	12.223%	$11.1437	$11.14	$11.15	$11.10
Purchase #2	$43.55	4.634%	$45.5681	$45.57	$45.55	$45.60
Purchase #3	$6.57	11.123%	$7.3008	$7.30	$7.30	$7.30
Purchase #4	$93.97	6.178%	$99.7755	$99.78	$99.80	$99.80
Purchase #5	$229.49	12.371%	$257.8802	$257.88	$257.90	$257.90
Purchase #6	$41.59	9.158%	$45.3988	$45.40	$45.40	$45.40
Purchase #7	$27.39	10.113%	$30.16	$30.16	$30.15	$30.20
7 purchase totals =	$452.49		$497.2271	$497.23	$497.25	$497.30