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	$18.92	11.578%	$21.1106	$21.11	$21.10	$21.10
Purchase #2	$31.76	12.126%	$35.6112	$35.61	$35.60	$35.60
Purchase #3	$50.48	13.204%	$57.1454	$57.15	$57.15	$57.10
Purchase #4	$177.55	7.399%	$190.6869	$190.69	$190.70	$190.70
Purchase #5	$72.33	9.154%	$78.9511	$78.95	$78.95	$79.00
Purchase #6	$105.61	7.113%	$113.122	$113.12	$113.10	$113.10
Purchase #7	$107.81	3.276%	$111.3419	$111.34	$111.35	$111.30
7 purchase totals =	$564.46		$607.9691	$607.97	$607.95	$607.90