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	$170.83	6.222%	$181.459	$181.46	$181.45	$181.50
Purchase #2	$189.96	13.563%	$215.7243	$215.72	$215.70	$215.70
Purchase #3	$35.72	12.709%	$40.2597	$40.26	$40.25	$40.30
Purchase #4	$196.42	7.502%	$211.1554	$211.16	$211.15	$211.20
Purchase #5	$57.75	11.520%	$64.4028	$64.40	$64.40	$64.40
Purchase #6	$56.92	6.665%	$60.7137	$60.71	$60.70	$60.70
Purchase #7	$192.71	8.868%	$209.7995	$209.80	$209.80	$209.80
7 purchase totals =	$900.31		$983.5144	$983.51	$983.45	$983.60