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	$47.50	9.388%	$51.9593	$51.96	$51.95	$52.00
Purchase #2	$183.49	3.867%	$190.5856	$190.59	$190.60	$190.60
Purchase #3	$109.47	10.438%	$120.8965	$120.90	$120.90	$120.90
Purchase #4	$71.82	3.656%	$74.4457	$74.45	$74.45	$74.40
Purchase #5	$91.59	13.433%	$103.8933	$103.89	$103.90	$103.90
Purchase #6	$158.63	9.801%	$174.1773	$174.18	$174.20	$174.20
Purchase #7	$93.93	12.301%	$105.4843	$105.48	$105.50	$105.50
7 purchase totals =	$756.43		$821.4420	$821.45	$821.50	$821.50