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	$73.84	12.749%	$83.2539	$83.25	$83.25	$83.30
Purchase #2	$135.76	5.276%	$142.9227	$142.92	$142.90	$142.90
Purchase #3	$111.52	10.861%	$123.6322	$123.63	$123.65	$123.60
Purchase #4	$79.28	13.306%	$89.829	$89.83	$89.85	$89.80
Purchase #5	$162.39	6.178%	$172.4225	$172.42	$172.40	$172.40
Purchase #6	$150.29	4.249%	$156.6758	$156.68	$156.70	$156.70
Purchase #7	$228.25	11.455%	$254.396	$254.40	$254.40	$254.40
7 purchase totals =	$941.33		$1,023.1321	$1,023.13	$1,023.15	$1,023.10