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	$96.50	13.866%	$109.8807	$109.88	$109.90	$109.90
Purchase #2	$88.40	4.523%	$92.3983	$92.40	$92.40	$92.40
Purchase #3	$36.50	5.832%	$38.6287	$38.63	$38.65	$38.60
Purchase #4	$194.49	8.547%	$211.1131	$211.11	$211.10	$211.10
Purchase #5	$246.70	9.611%	$270.4103	$270.41	$270.40	$270.40
Purchase #6	$185.89	7.788%	$200.3671	$200.37	$200.35	$200.40
Purchase #7	$49.29	9.176%	$53.8129	$53.81	$53.80	$53.80
7 purchase totals =	$897.77		$976.6111	$976.61	$976.60	$976.60