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	$6.66	5.776%	$7.0447	$7.04	$7.05	$7.00
Purchase #2	$50.65	10.327%	$55.8806	$55.88	$55.90	$55.90
Purchase #3	$136.35	6.172%	$144.7655	$144.77	$144.75	$144.80
Purchase #4	$183.28	5.609%	$193.5602	$193.56	$193.55	$193.60
Purchase #5	$38.61	9.744%	$42.3722	$42.37	$42.35	$42.40
Purchase #6	$95.33	8.865%	$103.781	$103.78	$103.80	$103.80
Purchase #7	$12.54	11.561%	$13.9897	$13.99	$14.00	$14.00
7 purchase totals =	$523.42		$561.3939	$561.39	$561.40	$561.50