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	$244.57	13.193%	$276.8361	$276.84	$276.85	$276.80
Purchase #2	$180.99	10.838%	$200.6057	$200.61	$200.60	$200.60
Purchase #3	$86.78	13.337%	$98.3538	$98.35	$98.35	$98.40
Purchase #4	$102.35	9.322%	$111.8911	$111.89	$111.90	$111.90
Purchase #5	$28.64	9.640%	$31.4009	$31.40	$31.40	$31.40
Purchase #6	$194.90	9.869%	$214.1347	$214.13	$214.15	$214.10
Purchase #7	$238.41	6.287%	$253.3988	$253.40	$253.40	$253.40
7 purchase totals =	$1,076.64		$1,186.6211	$1,186.62	$1,186.65	$1,186.60