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	$79.57	8.443%	$86.2881	$86.29	$86.30	$86.30
Purchase #2	$72.67	4.778%	$76.1422	$76.14	$76.15	$76.10
Purchase #3	$220.71	3.689%	$228.852	$228.85	$228.85	$228.90
Purchase #4	$26.50	11.118%	$29.4463	$29.45	$29.45	$29.40
Purchase #5	$197.97	10.282%	$218.3253	$218.33	$218.35	$218.30
Purchase #6	$33.68	6.568%	$35.8921	$35.89	$35.90	$35.90
Purchase #7	$127.59	3.820%	$132.4639	$132.46	$132.45	$132.50
7 purchase totals =	$758.69		$807.4099	$807.41	$807.45	$807.40