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	$242.96	11.231%	$270.2468	$270.25	$270.25	$270.20
Purchase #2	$174.34	4.297%	$181.8314	$181.83	$181.85	$181.80
Purchase #3	$98.67	12.638%	$111.1399	$111.14	$111.15	$111.10
Purchase #4	$56.50	8.217%	$61.1426	$61.14	$61.15	$61.10
Purchase #5	$65.88	9.791%	$72.3303	$72.33	$72.35	$72.30
Purchase #6	$12.59	3.371%	$13.0144	$13.01	$13.00	$13.00
Purchase #7	$26.85	8.519%	$29.1374	$29.14	$29.15	$29.10
7 purchase totals =	$677.79		$738.8428	$738.84	$738.90	$738.60