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	$127.84	6.855%	$136.6034	$136.60	$136.60	$136.60
Purchase #2	$101.66	9.284%	$111.0981	$111.10	$111.10	$111.10
Purchase #3	$211.63	5.631%	$223.5469	$223.55	$223.55	$223.50
Purchase #4	$79.68	13.342%	$90.3109	$90.31	$90.30	$90.30
Purchase #5	$211.33	13.822%	$240.54	$240.54	$240.55	$240.50
Purchase #6	$108.69	5.636%	$114.8158	$114.82	$114.80	$114.80
Purchase #7	$7.85	10.152%	$8.6469	$8.65	$8.65	$8.60
7 purchase totals =	$848.68		$925.5620	$925.57	$925.55	$925.40