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	$47.73	8.649%	$51.8582	$51.86	$51.85	$51.90
Purchase #2	$231.65	4.828%	$242.8341	$242.83	$242.85	$242.80
Purchase #3	$30.68	9.636%	$33.6363	$33.64	$33.65	$33.60
Purchase #4	$33.89	12.572%	$38.1507	$38.15	$38.15	$38.20
Purchase #5	$181.35	11.418%	$202.0565	$202.06	$202.05	$202.10
Purchase #6	$55.66	6.254%	$59.141	$59.14	$59.15	$59.10
Purchase #7	$142.75	7.819%	$153.9116	$153.91	$153.90	$153.90
7 purchase totals =	$723.71		$781.5884	$781.59	$781.60	$781.60