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	$134.93	7.393%	$144.9054	$144.91	$144.90	$144.90
Purchase #2	$31.36	13.296%	$35.5296	$35.53	$35.55	$35.50
Purchase #3	$34.98	9.326%	$38.2422	$38.24	$38.25	$38.20
Purchase #4	$226.41	7.211%	$242.7364	$242.74	$242.75	$242.70
Purchase #5	$141.40	7.207%	$151.5907	$151.59	$151.60	$151.60
Purchase #6	$155.59	10.766%	$172.3408	$172.34	$172.35	$172.30
Purchase #7	$126.73	12.613%	$142.7145	$142.71	$142.70	$142.70
7 purchase totals =	$851.40		$928.0596	$928.06	$928.10	$927.90