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	$136.77	8.415%	$148.2792	$148.28	$148.30	$148.30
Purchase #2	$126.45	8.681%	$137.4271	$137.43	$137.45	$137.40
Purchase #3	$83.41	10.737%	$92.3657	$92.37	$92.35	$92.40
Purchase #4	$244.38	12.869%	$275.8293	$275.83	$275.85	$275.80
Purchase #5	$42.89	13.827%	$48.8204	$48.82	$48.80	$48.80
Purchase #6	$97.67	6.747%	$104.2598	$104.26	$104.25	$104.30
Purchase #7	$220.92	13.236%	$250.161	$250.16	$250.15	$250.20
7 purchase totals =	$952.49		$1,057.1425	$1,057.15	$1,057.15	$1,057.20