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	$139.48	10.864%	$154.6331	$154.63	$154.65	$154.60
Purchase #2	$240.53	7.608%	$258.8295	$258.83	$258.85	$258.80
Purchase #3	$135.71	7.214%	$145.5001	$145.50	$145.50	$145.50
Purchase #4	$71.92	10.503%	$79.4738	$79.47	$79.45	$79.50
Purchase #5	$100.64	11.104%	$111.8151	$111.82	$111.80	$111.80
Purchase #6	$20.66	8.712%	$22.4599	$22.46	$22.45	$22.50
Purchase #7	$188.26	5.418%	$198.4599	$198.46	$198.45	$198.50
7 purchase totals =	$897.20		$971.1714	$971.17	$971.15	$971.20