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	$154.45	6.451%	$164.4136	$164.41	$164.40	$164.40
Purchase #2	$191.80	10.527%	$211.9908	$211.99	$212.00	$212.00
Purchase #3	$33.75	4.748%	$35.3525	$35.35	$35.35	$35.40
Purchase #4	$229.91	13.830%	$261.7066	$261.71	$261.70	$261.70
Purchase #5	$183.55	3.517%	$190.0055	$190.01	$190.00	$190.00
Purchase #6	$127.36	11.674%	$142.228	$142.23	$142.25	$142.20
Purchase #7	$69.88	11.712%	$78.0643	$78.06	$78.05	$78.10
7 purchase totals =	$990.70		$1,083.7613	$1,083.76	$1,083.75	$1,083.80