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	$225.98	11.340%	$251.6061	$251.61	$251.60	$251.60
Purchase #2	$82.68	9.467%	$90.5073	$90.51	$90.50	$90.50
Purchase #3	$227.76	6.377%	$242.2843	$242.28	$242.30	$242.30
Purchase #4	$93.80	5.120%	$98.6026	$98.60	$98.60	$98.60
Purchase #5	$216.70	4.682%	$226.8459	$226.85	$226.85	$226.80
Purchase #6	$56.39	10.510%	$62.3166	$62.32	$62.30	$62.30
Purchase #7	$14.62	4.823%	$15.3251	$15.33	$15.35	$15.30
7 purchase totals =	$917.93		$987.4879	$987.50	$987.50	$987.40