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	$185.89	12.448%	$209.0296	$209.03	$209.05	$209.00
Purchase #2	$82.58	8.846%	$89.885	$89.89	$89.90	$89.90
Purchase #3	$129.86	5.764%	$137.3451	$137.35	$137.35	$137.30
Purchase #4	$184.55	7.119%	$197.6881	$197.69	$197.70	$197.70
Purchase #5	$23.31	6.193%	$24.7536	$24.75	$24.75	$24.80
Purchase #6	$17.47	8.234%	$18.9085	$18.91	$18.90	$18.90
Purchase #7	$70.71	10.846%	$78.3792	$78.38	$78.40	$78.40
7 purchase totals =	$694.37		$755.9891	$756.00	$756.05	$756.00