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	$12.63	10.211%	$13.9196	$13.92	$13.90	$13.90
Purchase #2	$236.85	11.506%	$264.102	$264.10	$264.10	$264.10
Purchase #3	$22.33	11.338%	$24.8618	$24.86	$24.85	$24.90
Purchase #4	$54.70	11.558%	$61.0222	$61.02	$61.00	$61.00
Purchase #5	$150.31	5.696%	$158.8717	$158.87	$158.85	$158.90
Purchase #6	$77.77	4.444%	$81.2261	$81.23	$81.25	$81.20
Purchase #7	$69.94	12.412%	$78.621	$78.62	$78.60	$78.60
7 purchase totals =	$624.53		$682.6244	$682.62	$682.55	$682.60