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	$79.91	3.300%	$82.547	$82.55	$82.55	$82.50
Purchase #2	$166.51	8.336%	$180.3903	$180.39	$180.40	$180.40
Purchase #3	$140.76	4.731%	$147.4194	$147.42	$147.40	$147.40
Purchase #4	$184.52	3.141%	$190.3158	$190.32	$190.30	$190.30
Purchase #5	$173.49	12.730%	$195.5753	$195.58	$195.60	$195.60
Purchase #6	$221.28	10.608%	$244.7534	$244.75	$244.75	$244.80
Purchase #7	$39.79	7.702%	$42.8546	$42.85	$42.85	$42.90
7 purchase totals =	$1,006.26		$1,083.8558	$1,083.86	$1,083.85	$1,083.90