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	$140.80	11.230%	$156.6118	$156.61	$156.60	$156.60
Purchase #2	$123.79	13.365%	$140.3345	$140.33	$140.35	$140.30
Purchase #3	$178.25	7.194%	$191.0733	$191.07	$191.05	$191.10
Purchase #4	$70.97	12.334%	$79.7234	$79.72	$79.70	$79.70
Purchase #5	$39.69	11.236%	$44.1496	$44.15	$44.15	$44.10
Purchase #6	$46.86	13.397%	$53.1378	$53.14	$53.15	$53.10
Purchase #7	$99.59	9.327%	$108.8788	$108.88	$108.90	$108.90
7 purchase totals =	$699.95		$773.9092	$773.90	$773.90	$773.80