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	$58.27	5.870%	$61.6904	$61.69	$61.70	$61.70
Purchase #2	$38.45	10.674%	$42.5542	$42.55	$42.55	$42.60
Purchase #3	$234.84	12.237%	$263.5774	$263.58	$263.60	$263.60
Purchase #4	$218.50	11.745%	$244.1628	$244.16	$244.15	$244.20
Purchase #5	$150.70	10.565%	$166.6215	$166.62	$166.60	$166.60
Purchase #6	$233.68	13.116%	$264.3295	$264.33	$264.35	$264.30
Purchase #7	$71.70	8.704%	$77.9408	$77.94	$77.95	$77.90
7 purchase totals =	$1,006.14		$1,120.8766	$1,120.87	$1,120.90	$1,120.90