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	$77.72	5.122%	$81.7008	$81.70	$81.70	$81.70
Purchase #2	$198.61	5.529%	$209.5911	$209.59	$209.60	$209.60
Purchase #3	$116.38	11.536%	$129.8056	$129.81	$129.80	$129.80
Purchase #4	$205.76	8.231%	$222.6961	$222.70	$222.70	$222.70
Purchase #5	$232.56	8.202%	$251.6346	$251.63	$251.65	$251.60
Purchase #6	$100.64	5.818%	$106.4952	$106.50	$106.50	$106.50
Purchase #7	$81.92	9.366%	$89.5926	$89.59	$89.60	$89.60
7 purchase totals =	$1,013.59		$1,091.5160	$1,091.52	$1,091.55	$1,091.50