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	$78.46	7.589%	$84.4143	$84.41	$84.40	$84.40
Purchase #2	$210.36	6.291%	$223.5937	$223.59	$223.60	$223.60
Purchase #3	$147.52	4.297%	$153.8589	$153.86	$153.85	$153.90
Purchase #4	$31.57	13.640%	$35.8761	$35.88	$35.90	$35.90
Purchase #5	$234.76	5.611%	$247.9324	$247.93	$247.95	$247.90
Purchase #6	$142.39	4.240%	$148.4273	$148.43	$148.45	$148.40
Purchase #7	$40.44	13.871%	$46.0494	$46.05	$46.05	$46.00
7 purchase totals =	$885.50		$940.1521	$940.15	$940.20	$940.10