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	$37.69	13.614%	$42.8211	$42.82	$42.80	$42.80
Purchase #2	$143.77	5.409%	$151.5465	$151.55	$151.55	$151.50
Purchase #3	$146.88	6.358%	$156.2186	$156.22	$156.20	$156.20
Purchase #4	$155.90	7.232%	$167.1747	$167.17	$167.15	$167.20
Purchase #5	$69.73	9.119%	$76.0887	$76.09	$76.10	$76.10
Purchase #6	$184.49	5.224%	$194.1278	$194.13	$194.15	$194.10
Purchase #7	$51.34	13.627%	$58.3361	$58.34	$58.35	$58.30
7 purchase totals =	$789.80		$846.3135	$846.32	$846.30	$846.20