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	$120.51	8.641%	$130.9233	$130.92	$130.90	$130.90
Purchase #2	$73.84	11.817%	$82.5657	$82.57	$82.55	$82.60
Purchase #3	$148.66	12.451%	$167.1697	$167.17	$167.15	$167.20
Purchase #4	$75.30	4.406%	$78.6177	$78.62	$78.60	$78.60
Purchase #5	$61.69	8.631%	$67.0145	$67.01	$67.00	$67.00
Purchase #6	$158.70	6.748%	$169.4091	$169.41	$169.40	$169.40
Purchase #7	$13.52	12.183%	$15.1671	$15.17	$15.15	$15.20
7 purchase totals =	$652.22		$710.8671	$710.87	$710.75	$710.90