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	$191.45	6.792%	$204.4533	$204.45	$204.45	$204.50
Purchase #2	$118.40	5.254%	$124.6207	$124.62	$124.60	$124.60
Purchase #3	$179.54	11.576%	$200.3236	$200.32	$200.30	$200.30
Purchase #4	$181.86	13.478%	$206.3711	$206.37	$206.35	$206.40
Purchase #5	$219.29	10.349%	$241.9843	$241.98	$242.00	$242.00
Purchase #6	$81.28	11.233%	$90.4102	$90.41	$90.40	$90.40
Purchase #7	$13.72	4.721%	$14.3677	$14.37	$14.35	$14.40
7 purchase totals =	$985.54		$1,082.5309	$1,082.52	$1,082.45	$1,082.60