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	$48.38	13.742%	$55.0284	$55.03	$55.05	$55.00
Purchase #2	$75.40	13.329%	$85.4501	$85.45	$85.45	$85.50
Purchase #3	$232.34	5.740%	$245.6763	$245.68	$245.70	$245.70
Purchase #4	$50.72	9.184%	$55.3781	$55.38	$55.40	$55.40
Purchase #5	$100.55	13.516%	$114.1403	$114.14	$114.15	$114.10
Purchase #6	$78.73	12.766%	$88.7807	$88.78	$88.80	$88.80
Purchase #7	$169.78	12.277%	$190.6239	$190.62	$190.60	$190.60
7 purchase totals =	$755.90		$835.0778	$835.08	$835.15	$835.10