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	$244.82	9.719%	$268.6141	$268.61	$268.60	$268.60
Purchase #2	$46.99	7.213%	$50.3794	$50.38	$50.40	$50.40
Purchase #3	$89.70	5.258%	$94.4164	$94.42	$94.40	$94.40
Purchase #4	$41.69	3.206%	$43.0266	$43.03	$43.05	$43.00
Purchase #5	$240.65	4.658%	$251.8595	$251.86	$251.85	$251.90
Purchase #6	$58.40	5.522%	$61.6248	$61.62	$61.60	$61.60
Purchase #7	$153.26	6.317%	$162.9414	$162.94	$162.95	$162.90
7 purchase totals =	$875.51		$932.8622	$932.86	$932.85	$932.80