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	$230.45	8.301%	$249.5797	$249.58	$249.60	$249.60
Purchase #2	$90.62	5.761%	$95.8406	$95.84	$95.85	$95.80
Purchase #3	$166.77	4.530%	$174.3247	$174.32	$174.30	$174.30
Purchase #4	$44.34	3.341%	$45.8214	$45.82	$45.80	$45.80
Purchase #5	$11.73	11.296%	$13.055	$13.06	$13.05	$13.10
Purchase #6	$83.79	7.689%	$90.2326	$90.23	$90.25	$90.20
Purchase #7	$156.60	4.792%	$164.1043	$164.10	$164.10	$164.10
7 purchase totals =	$784.30		$832.9583	$832.95	$832.95	$832.90