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	$245.26	3.847%	$254.6952	$254.70	$254.70	$254.70
Purchase #2	$30.34	10.564%	$33.5451	$33.55	$33.55	$33.50
Purchase #3	$38.85	6.743%	$41.4697	$41.47	$41.45	$41.50
Purchase #4	$143.82	3.287%	$148.5474	$148.55	$148.55	$148.50
Purchase #5	$139.27	11.382%	$155.1217	$155.12	$155.10	$155.10
Purchase #6	$193.61	11.209%	$215.3117	$215.31	$215.30	$215.30
Purchase #7	$92.52	8.798%	$100.6599	$100.66	$100.65	$100.70
7 purchase totals =	$883.67		$949.3507	$949.36	$949.30	$949.30