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	$100.89	3.205%	$104.1235	$104.12	$104.10	$104.10
Purchase #2	$156.77	10.108%	$172.6163	$172.62	$172.60	$172.60
Purchase #3	$115.55	12.335%	$129.8031	$129.80	$129.80	$129.80
Purchase #4	$24.47	12.393%	$27.5026	$27.50	$27.50	$27.50
Purchase #5	$212.52	7.697%	$228.8777	$228.88	$228.90	$228.90
Purchase #6	$148.67	11.560%	$165.8563	$165.86	$165.85	$165.90
Purchase #7	$104.97	7.560%	$112.9057	$112.91	$112.90	$112.90
7 purchase totals =	$863.84		$941.6852	$941.69	$941.65	$941.70