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	$156.65	6.722%	$167.18	$167.18	$167.20	$167.20
Purchase #2	$200.83	6.252%	$213.3859	$213.39	$213.40	$213.40
Purchase #3	$147.64	6.314%	$156.962	$156.96	$156.95	$157.00
Purchase #4	$142.68	6.717%	$152.2638	$152.26	$152.25	$152.30
Purchase #5	$188.32	13.360%	$213.4796	$213.48	$213.50	$213.50
Purchase #6	$181.81	12.821%	$205.1199	$205.12	$205.10	$205.10
Purchase #7	$158.54	8.600%	$172.1744	$172.17	$172.15	$172.20
7 purchase totals =	$1,176.47		$1,280.5656	$1,280.56	$1,280.55	$1,280.70