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	$50.62	9.229%	$55.2917	$55.29	$55.30	$55.30
Purchase #2	$144.31	11.432%	$160.8075	$160.81	$160.80	$160.80
Purchase #3	$174.60	7.758%	$188.1455	$188.15	$188.15	$188.10
Purchase #4	$66.78	9.126%	$72.8743	$72.87	$72.85	$72.90
Purchase #5	$118.40	3.322%	$122.3332	$122.33	$122.35	$122.30
Purchase #6	$63.93	5.733%	$67.5951	$67.60	$67.60	$67.60
Purchase #7	$82.64	10.586%	$91.3883	$91.39	$91.40	$91.40
7 purchase totals =	$701.28		$758.4356	$758.44	$758.45	$758.40