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	$38.87	5.386%	$40.9635	$40.96	$40.95	$41.00
Purchase #2	$46.37	11.242%	$51.5829	$51.58	$51.60	$51.60
Purchase #3	$197.49	13.125%	$223.4106	$223.41	$223.40	$223.40
Purchase #4	$127.80	11.314%	$142.2593	$142.26	$142.25	$142.30
Purchase #5	$71.68	12.846%	$80.888	$80.89	$80.90	$80.90
Purchase #6	$152.35	5.346%	$160.4946	$160.49	$160.50	$160.50
Purchase #7	$91.30	12.282%	$102.5135	$102.51	$102.50	$102.50
7 purchase totals =	$725.86		$802.1124	$802.10	$802.10	$802.20