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	$111.43	3.586%	$115.4259	$115.43	$115.45	$115.40
Purchase #2	$188.56	6.312%	$200.4619	$200.46	$200.45	$200.50
Purchase #3	$239.82	5.750%	$253.6097	$253.61	$253.60	$253.60
Purchase #4	$160.66	5.857%	$170.0699	$170.07	$170.05	$170.10
Purchase #5	$36.73	7.528%	$39.495	$39.50	$39.50	$39.50
Purchase #6	$94.69	6.393%	$100.7435	$100.74	$100.75	$100.70
Purchase #7	$100.33	4.160%	$104.5037	$104.50	$104.50	$104.50
7 purchase totals =	$932.22		$984.3096	$984.31	$984.30	$984.30