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	$68.82	13.668%	$78.2263	$78.23	$78.25	$78.20
Purchase #2	$130.43	4.815%	$136.7102	$136.71	$136.70	$136.70
Purchase #3	$33.28	9.358%	$36.3943	$36.39	$36.40	$36.40
Purchase #4	$104.41	11.476%	$116.3921	$116.39	$116.40	$116.40
Purchase #5	$6.83	3.779%	$7.0881	$7.09	$7.10	$7.10
Purchase #6	$99.35	12.420%	$111.6893	$111.69	$111.70	$111.70
Purchase #7	$246.30	8.586%	$267.4473	$267.45	$267.45	$267.40
7 purchase totals =	$689.42		$753.9476	$753.95	$754.00	$753.90