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	$77.79	9.398%	$85.1007	$85.10	$85.10	$85.10
Purchase #2	$43.69	4.364%	$45.5966	$45.60	$45.60	$45.60
Purchase #3	$194.25	6.361%	$206.6062	$206.61	$206.60	$206.60
Purchase #4	$89.60	10.417%	$98.9336	$98.93	$98.95	$98.90
Purchase #5	$234.41	9.115%	$255.7765	$255.78	$255.80	$255.80
Purchase #6	$101.93	7.158%	$109.2261	$109.23	$109.25	$109.20
Purchase #7	$172.54	10.392%	$190.4704	$190.47	$190.45	$190.50
7 purchase totals =	$914.21		$991.7101	$991.72	$991.75	$991.70