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	$46.89	6.145%	$49.7714	$49.77	$49.75	$49.80
Purchase #2	$237.25	7.766%	$255.6748	$255.67	$255.65	$255.70
Purchase #3	$40.25	4.160%	$41.9244	$41.92	$41.90	$41.90
Purchase #4	$29.70	13.714%	$33.7731	$33.77	$33.75	$33.80
Purchase #5	$250.45	11.862%	$280.1584	$280.16	$280.15	$280.20
Purchase #6	$171.91	7.717%	$185.1763	$185.18	$185.20	$185.20
Purchase #7	$186.44	4.208%	$194.2854	$194.29	$194.30	$194.30
7 purchase totals =	$962.89		$1,040.7638	$1,040.76	$1,040.70	$1,040.90