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	$19.70	7.325%	$21.143	$21.14	$21.15	$21.10
Purchase #2	$225.93	6.797%	$241.2865	$241.29	$241.30	$241.30
Purchase #3	$162.89	5.783%	$172.3099	$172.31	$172.30	$172.30
Purchase #4	$231.32	5.848%	$244.8476	$244.85	$244.85	$244.80
Purchase #5	$174.36	8.809%	$189.7194	$189.72	$189.70	$189.70
Purchase #6	$17.93	5.188%	$18.8602	$18.86	$18.85	$18.90
Purchase #7	$70.33	3.488%	$72.7831	$72.78	$72.80	$72.80
7 purchase totals =	$902.46		$960.9497	$960.95	$960.95	$960.90