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	$236.62	6.271%	$251.4584	$251.46	$251.45	$251.50
Purchase #2	$52.51	6.771%	$56.0655	$56.07	$56.05	$56.10
Purchase #3	$37.36	5.469%	$39.4032	$39.40	$39.40	$39.40
Purchase #4	$152.47	5.215%	$160.4213	$160.42	$160.40	$160.40
Purchase #5	$190.69	10.382%	$210.4874	$210.49	$210.50	$210.50
Purchase #6	$82.43	11.170%	$91.6374	$91.64	$91.65	$91.60
Purchase #7	$56.78	8.282%	$61.4825	$61.48	$61.50	$61.50
7 purchase totals =	$808.86		$870.9557	$870.96	$870.95	$871.00