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	$102.46	4.211%	$106.7746	$106.77	$106.75	$106.80
Purchase #2	$78.31	9.341%	$85.6249	$85.62	$85.60	$85.60
Purchase #3	$227.96	3.602%	$236.1711	$236.17	$236.15	$236.20
Purchase #4	$20.94	7.314%	$22.4716	$22.47	$22.45	$22.50
Purchase #5	$173.65	13.149%	$196.4832	$196.48	$196.50	$196.50
Purchase #6	$148.68	3.801%	$154.3313	$154.33	$154.35	$154.30
Purchase #7	$150.53	11.783%	$168.2669	$168.27	$168.25	$168.30
7 purchase totals =	$902.53		$970.1236	$970.11	$970.05	$970.20