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	$137.54	13.191%	$155.6829	$155.68	$155.70	$155.70
Purchase #2	$217.79	10.401%	$240.4423	$240.44	$240.45	$240.40
Purchase #3	$154.35	11.317%	$171.8178	$171.82	$171.80	$171.80
Purchase #4	$137.49	10.372%	$151.7505	$151.75	$151.75	$151.80
Purchase #5	$219.26	10.259%	$241.7539	$241.75	$241.75	$241.80
Purchase #6	$139.52	8.649%	$151.5871	$151.59	$151.60	$151.60
Purchase #7	$34.74	7.719%	$37.4216	$37.42	$37.40	$37.40
7 purchase totals =	$1,040.69		$1,150.4561	$1,150.45	$1,150.45	$1,150.50