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	$89.90	11.649%	$100.3725	$100.37	$100.35	$100.40
Purchase #2	$213.66	13.572%	$242.6579	$242.66	$242.65	$242.70
Purchase #3	$212.86	5.114%	$223.7457	$223.75	$223.75	$223.70
Purchase #4	$151.91	7.227%	$162.8885	$162.89	$162.90	$162.90
Purchase #5	$67.40	11.596%	$75.2157	$75.22	$75.20	$75.20
Purchase #6	$87.51	6.851%	$93.5053	$93.51	$93.50	$93.50
Purchase #7	$195.97	8.533%	$212.6921	$212.69	$212.70	$212.70
7 purchase totals =	$1,019.21		$1,111.0777	$1,111.09	$1,111.05	$1,111.10