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	$55.79	6.797%	$59.582	$59.58	$59.60	$59.60
Purchase #2	$192.99	12.727%	$217.5518	$217.55	$217.55	$217.60
Purchase #3	$136.41	4.690%	$142.8076	$142.81	$142.80	$142.80
Purchase #4	$63.58	3.183%	$65.6038	$65.60	$65.60	$65.60
Purchase #5	$166.93	11.760%	$186.561	$186.56	$186.55	$186.60
Purchase #6	$150.93	10.313%	$166.4954	$166.50	$166.50	$166.50
Purchase #7	$141.57	8.716%	$153.9092	$153.91	$153.90	$153.90
7 purchase totals =	$908.20		$992.5108	$992.51	$992.50	$992.60