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	$110.46	10.861%	$122.4571	$122.46	$122.45	$122.50
Purchase #2	$139.66	11.751%	$156.0714	$156.07	$156.05	$156.10
Purchase #3	$123.52	3.227%	$127.506	$127.51	$127.50	$127.50
Purchase #4	$147.90	6.404%	$157.3715	$157.37	$157.35	$157.40
Purchase #5	$27.62	4.864%	$28.9634	$28.96	$28.95	$29.00
Purchase #6	$58.38	6.868%	$62.3895	$62.39	$62.40	$62.40
Purchase #7	$6.46	10.159%	$7.1163	$7.12	$7.10	$7.10
7 purchase totals =	$614.00		$661.8752	$661.88	$661.80	$662.00