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	$75.91	8.794%	$82.5855	$82.59	$82.60	$82.60
Purchase #2	$61.86	4.716%	$64.7773	$64.78	$64.80	$64.80
Purchase #3	$181.37	12.759%	$204.511	$204.51	$204.50	$204.50
Purchase #4	$80.27	12.671%	$90.441	$90.44	$90.45	$90.40
Purchase #5	$128.56	13.290%	$145.6456	$145.65	$145.65	$145.60
Purchase #6	$13.60	11.394%	$15.1496	$15.15	$15.15	$15.10
Purchase #7	$33.96	4.218%	$35.3924	$35.39	$35.40	$35.40
7 purchase totals =	$575.53		$638.5024	$638.51	$638.55	$638.40