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	$62.92	7.329%	$67.5314	$67.53	$67.55	$67.50
Purchase #2	$82.71	9.554%	$90.6121	$90.61	$90.60	$90.60
Purchase #3	$58.34	10.436%	$64.4284	$64.43	$64.45	$64.40
Purchase #4	$50.64	13.334%	$57.3923	$57.39	$57.40	$57.40
Purchase #5	$134.61	8.650%	$146.2538	$146.25	$146.25	$146.30
Purchase #6	$92.34	4.358%	$96.3642	$96.36	$96.35	$96.40
Purchase #7	$98.85	12.355%	$111.0629	$111.06	$111.05	$111.10
7 purchase totals =	$580.41		$633.6451	$633.63	$633.65	$633.70