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	$46.50	8.740%	$50.5641	$50.56	$50.55	$50.60
Purchase #2	$95.96	7.704%	$103.3528	$103.35	$103.35	$103.40
Purchase #3	$52.92	8.697%	$57.5225	$57.52	$57.50	$57.50
Purchase #4	$129.40	3.400%	$133.7996	$133.80	$133.80	$133.80
Purchase #5	$47.97	9.486%	$52.5204	$52.52	$52.50	$52.50
Purchase #6	$19.42	5.470%	$20.4823	$20.48	$20.50	$20.50
Purchase #7	$85.58	11.704%	$95.5963	$95.60	$95.60	$95.60
7 purchase totals =	$477.75		$513.8380	$513.83	$513.80	$513.90