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	$232.76	13.540%	$264.2757	$264.28	$264.30	$264.30
Purchase #2	$236.72	10.245%	$260.972	$260.97	$260.95	$261.00
Purchase #3	$152.54	4.652%	$159.6362	$159.64	$159.65	$159.60
Purchase #4	$103.70	11.464%	$115.5882	$115.59	$115.60	$115.60
Purchase #5	$74.83	13.643%	$85.0391	$85.04	$85.05	$85.00
Purchase #6	$57.27	9.765%	$62.8624	$62.86	$62.85	$62.90
Purchase #7	$39.82	7.561%	$42.8308	$42.83	$42.85	$42.80
7 purchase totals =	$897.64		$991.2044	$991.21	$991.25	$991.20