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	$15.48	7.859%	$16.6966	$16.70	$16.70	$16.70
Purchase #2	$50.78	10.361%	$56.0413	$56.04	$56.05	$56.00
Purchase #3	$102.50	7.824%	$110.5196	$110.52	$110.50	$110.50
Purchase #4	$171.36	8.255%	$185.5058	$185.51	$185.50	$185.50
Purchase #5	$190.72	3.139%	$196.7067	$196.71	$196.70	$196.70
Purchase #6	$174.56	11.542%	$194.7077	$194.71	$194.70	$194.70
Purchase #7	$248.83	11.775%	$278.1297	$278.13	$278.15	$278.10
7 purchase totals =	$954.23		$1,038.3074	$1,038.32	$1,038.30	$1,038.20