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	$145.51	5.349%	$153.2933	$153.29	$153.30	$153.30
Purchase #2	$213.39	11.329%	$237.565	$237.57	$237.55	$237.60
Purchase #3	$79.87	11.472%	$89.0327	$89.03	$89.05	$89.00
Purchase #4	$183.93	5.565%	$194.1657	$194.17	$194.15	$194.20
Purchase #5	$61.97	8.816%	$67.4333	$67.43	$67.45	$67.40
Purchase #6	$225.82	11.123%	$250.938	$250.94	$250.95	$250.90
Purchase #7	$6.40	11.386%	$7.1287	$7.13	$7.15	$7.10
7 purchase totals =	$916.89		$999.5567	$999.56	$999.60	$999.50