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	$5.76	8.592%	$6.2549	$6.25	$6.25	$6.30
Purchase #2	$11.62	10.352%	$12.8229	$12.82	$12.80	$12.80
Purchase #3	$51.31	6.172%	$54.4769	$54.48	$54.50	$54.50
Purchase #4	$53.84	13.832%	$61.2871	$61.29	$61.30	$61.30
Purchase #5	$163.33	5.537%	$172.3736	$172.37	$172.35	$172.40
Purchase #6	$53.31	7.450%	$57.2816	$57.28	$57.30	$57.30
Purchase #7	$136.34	13.656%	$154.9586	$154.96	$154.95	$155.00
7 purchase totals =	$475.51		$519.4556	$519.45	$519.45	$519.60