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	$50.61	3.810%	$52.5382	$52.54	$52.55	$52.50
Purchase #2	$157.53	8.832%	$171.443	$171.44	$171.45	$171.40
Purchase #3	$114.44	7.537%	$123.0653	$123.07	$123.05	$123.10
Purchase #4	$108.58	8.732%	$118.0612	$118.06	$118.05	$118.10
Purchase #5	$162.41	3.321%	$167.8036	$167.80	$167.80	$167.80
Purchase #6	$58.77	10.571%	$64.9826	$64.98	$65.00	$65.00
Purchase #7	$154.55	7.206%	$165.6869	$165.69	$165.70	$165.70
7 purchase totals =	$806.89		$863.5808	$863.58	$863.60	$863.60