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	$200.58	7.848%	$216.3215	$216.32	$216.30	$216.30
Purchase #2	$88.60	11.550%	$98.8333	$98.83	$98.85	$98.80
Purchase #3	$146.64	6.649%	$156.3901	$156.39	$156.40	$156.40
Purchase #4	$192.50	10.331%	$212.3872	$212.39	$212.40	$212.40
Purchase #5	$41.42	6.645%	$44.1724	$44.17	$44.15	$44.20
Purchase #6	$52.58	13.378%	$59.6142	$59.61	$59.60	$59.60
Purchase #7	$133.25	8.176%	$144.1445	$144.14	$144.15	$144.10
7 purchase totals =	$855.57		$931.8632	$931.85	$931.85	$931.80