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	$56.32	9.212%	$61.5082	$61.51	$61.50	$61.50
Purchase #2	$57.40	11.178%	$63.8162	$63.82	$63.80	$63.80
Purchase #3	$119.95	13.310%	$135.9153	$135.92	$135.90	$135.90
Purchase #4	$115.44	10.776%	$127.8798	$127.88	$127.90	$127.90
Purchase #5	$225.79	3.253%	$233.1349	$233.13	$233.15	$233.10
Purchase #6	$192.67	3.496%	$199.4057	$199.41	$199.40	$199.40
Purchase #7	$88.76	12.835%	$100.1523	$100.15	$100.15	$100.20
7 purchase totals =	$856.33		$921.8124	$921.82	$921.80	$921.80