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	$55.70	4.344%	$58.1196	$58.12	$58.10	$58.10
Purchase #2	$156.33	7.104%	$167.4357	$167.44	$167.45	$167.40
Purchase #3	$90.77	9.388%	$99.2915	$99.29	$99.30	$99.30
Purchase #4	$168.57	7.565%	$181.3223	$181.32	$181.30	$181.30
Purchase #5	$64.47	3.358%	$66.6349	$66.63	$66.65	$66.60
Purchase #6	$151.89	6.466%	$161.7112	$161.71	$161.70	$161.70
Purchase #7	$40.89	4.810%	$42.8568	$42.86	$42.85	$42.90
7 purchase totals =	$728.62		$777.3720	$777.37	$777.35	$777.30