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	$28.35	11.371%	$31.5737	$31.57	$31.55	$31.60
Purchase #2	$76.29	4.628%	$79.8207	$79.82	$79.80	$79.80
Purchase #3	$65.41	9.271%	$71.4742	$71.47	$71.45	$71.50
Purchase #4	$155.47	3.758%	$161.3126	$161.31	$161.30	$161.30
Purchase #5	$217.52	9.679%	$238.5738	$238.57	$238.55	$238.60
Purchase #6	$89.25	7.572%	$96.008	$96.01	$96.00	$96.00
Purchase #7	$57.63	7.813%	$62.1326	$62.13	$62.15	$62.10
7 purchase totals =	$689.92		$740.8956	$740.88	$740.80	$740.90