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	$53.78	6.824%	$57.4499	$57.45	$57.45	$57.40
Purchase #2	$90.30	3.500%	$93.4605	$93.46	$93.45	$93.50
Purchase #3	$242.62	4.590%	$253.7563	$253.76	$253.75	$253.80
Purchase #4	$163.42	4.491%	$170.7592	$170.76	$170.75	$170.80
Purchase #5	$90.44	13.139%	$102.3229	$102.32	$102.30	$102.30
Purchase #6	$153.76	12.129%	$172.4096	$172.41	$172.40	$172.40
Purchase #7	$111.53	11.468%	$124.3203	$124.32	$124.30	$124.30
7 purchase totals =	$905.85		$974.4787	$974.48	$974.40	$974.50