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	$160.89	4.712%	$168.4711	$168.47	$168.45	$168.50
Purchase #2	$149.43	3.501%	$154.6615	$154.66	$154.65	$154.70
Purchase #3	$68.51	4.738%	$71.756	$71.76	$71.75	$71.80
Purchase #4	$215.81	10.627%	$238.7441	$238.74	$238.75	$238.70
Purchase #5	$73.44	6.871%	$78.4861	$78.49	$78.50	$78.50
Purchase #6	$196.25	12.765%	$221.3013	$221.30	$221.30	$221.30
Purchase #7	$53.39	7.158%	$57.2117	$57.21	$57.20	$57.20
7 purchase totals =	$917.72		$990.6318	$990.63	$990.60	$990.70