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	$115.27	10.361%	$127.2131	$127.21	$127.20	$127.20
Purchase #2	$51.54	9.713%	$56.5461	$56.55	$56.55	$56.50
Purchase #3	$44.87	3.375%	$46.3844	$46.38	$46.40	$46.40
Purchase #4	$76.42	9.865%	$83.9588	$83.96	$83.95	$84.00
Purchase #5	$95.30	5.173%	$100.2299	$100.23	$100.25	$100.20
Purchase #6	$95.84	8.494%	$103.9806	$103.98	$104.00	$104.00
Purchase #7	$66.75	9.203%	$72.893	$72.89	$72.90	$72.90
7 purchase totals =	$545.99		$591.2059	$591.20	$591.25	$591.20