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	$147.77	13.752%	$168.0913	$168.09	$168.10	$168.10
Purchase #2	$239.54	12.846%	$270.3113	$270.31	$270.30	$270.30
Purchase #3	$186.42	7.348%	$200.1181	$200.12	$200.10	$200.10
Purchase #4	$144.49	9.819%	$158.6775	$158.68	$158.70	$158.70
Purchase #5	$26.95	4.641%	$28.2007	$28.20	$28.20	$28.20
Purchase #6	$129.86	13.596%	$147.5158	$147.52	$147.50	$147.50
Purchase #7	$160.82	11.308%	$179.0055	$179.01	$179.00	$179.00
7 purchase totals =	$1,035.85		$1,151.9202	$1,151.93	$1,151.90	$1,151.90