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	$40.84	3.385%	$42.2224	$42.22	$42.20	$42.20
Purchase #2	$38.84	9.149%	$42.3935	$42.39	$42.40	$42.40
Purchase #3	$155.42	10.841%	$172.2691	$172.27	$172.25	$172.30
Purchase #4	$178.83	6.344%	$190.175	$190.18	$190.20	$190.20
Purchase #5	$97.44	6.391%	$103.6674	$103.67	$103.65	$103.70
Purchase #6	$60.82	11.455%	$67.7869	$67.79	$67.80	$67.80
Purchase #7	$180.38	7.661%	$194.1989	$194.20	$194.20	$194.20
7 purchase totals =	$752.57		$812.7132	$812.72	$812.70	$812.80