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	$205.83	11.408%	$229.3111	$229.31	$229.30	$229.30
Purchase #2	$158.40	13.229%	$179.3547	$179.35	$179.35	$179.40
Purchase #3	$222.27	8.353%	$240.8362	$240.84	$240.85	$240.80
Purchase #4	$39.70	8.170%	$42.9435	$42.94	$42.95	$42.90
Purchase #5	$79.85	10.293%	$88.069	$88.07	$88.05	$88.10
Purchase #6	$9.85	7.310%	$10.57	$10.57	$10.55	$10.60
Purchase #7	$34.96	6.685%	$37.2971	$37.30	$37.30	$37.30
7 purchase totals =	$750.86		$828.3816	$828.38	$828.35	$828.40