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	$44.87	12.490%	$50.4743	$50.47	$50.45	$50.50
Purchase #2	$175.77	6.499%	$187.1933	$187.19	$187.20	$187.20
Purchase #3	$182.56	3.251%	$188.495	$188.50	$188.50	$188.50
Purchase #4	$64.56	9.778%	$70.8727	$70.87	$70.85	$70.90
Purchase #5	$72.70	12.279%	$81.6268	$81.63	$81.65	$81.60
Purchase #6	$130.51	9.164%	$142.4699	$142.47	$142.45	$142.50
Purchase #7	$43.33	7.865%	$46.7379	$46.74	$46.75	$46.70
7 purchase totals =	$714.30		$767.8699	$767.87	$767.85	$767.90