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	$52.82	6.563%	$56.2866	$56.29	$56.30	$56.30
Purchase #2	$190.70	9.390%	$208.6067	$208.61	$208.60	$208.60
Purchase #3	$237.41	6.766%	$253.4732	$253.47	$253.45	$253.50
Purchase #4	$62.86	13.432%	$71.3034	$71.30	$71.30	$71.30
Purchase #5	$194.48	8.157%	$210.3437	$210.34	$210.35	$210.30
Purchase #6	$204.94	8.469%	$222.2964	$222.30	$222.30	$222.30
Purchase #7	$53.55	10.325%	$59.079	$59.08	$59.10	$59.10
7 purchase totals =	$996.76		$1,081.3890	$1,081.39	$1,081.40	$1,081.40