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	$50.67	11.435%	$56.4641	$56.46	$56.45	$56.50
Purchase #2	$172.82	10.496%	$190.9592	$190.96	$190.95	$191.00
Purchase #3	$26.94	13.396%	$30.5489	$30.55	$30.55	$30.50
Purchase #4	$142.54	7.217%	$152.8271	$152.83	$152.85	$152.80
Purchase #5	$159.98	4.842%	$167.7262	$167.73	$167.75	$167.70
Purchase #6	$136.28	3.689%	$141.3074	$141.31	$141.30	$141.30
Purchase #7	$216.39	7.871%	$233.4221	$233.42	$233.40	$233.40
7 purchase totals =	$905.62		$973.2550	$973.26	$973.25	$973.20