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	$5.86	7.726%	$6.3127	$6.31	$6.30	$6.30
Purchase #2	$6.89	13.204%	$7.7998	$7.80	$7.80	$7.80
Purchase #3	$247.45	8.372%	$268.1665	$268.17	$268.15	$268.20
Purchase #4	$34.39	9.110%	$37.5229	$37.52	$37.50	$37.50
Purchase #5	$54.93	7.644%	$59.1288	$59.13	$59.15	$59.10
Purchase #6	$155.64	3.334%	$160.829	$160.83	$160.85	$160.80
Purchase #7	$207.57	5.838%	$219.6879	$219.69	$219.70	$219.70
7 purchase totals =	$712.73		$759.4476	$759.45	$759.45	$759.40