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	$64.97	7.777%	$70.0227	$70.02	$70.00	$70.00
Purchase #2	$218.70	13.633%	$248.5154	$248.52	$248.50	$248.50
Purchase #3	$175.85	8.403%	$190.6267	$190.63	$190.65	$190.60
Purchase #4	$211.64	4.440%	$221.0368	$221.04	$221.05	$221.00
Purchase #5	$74.90	5.134%	$78.7454	$78.75	$78.75	$78.70
Purchase #6	$60.34	11.517%	$67.2894	$67.29	$67.30	$67.30
Purchase #7	$244.29	10.285%	$269.4152	$269.42	$269.40	$269.40
7 purchase totals =	$1,050.69		$1,145.6516	$1,145.67	$1,145.65	$1,145.50