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	$82.56	9.690%	$90.5601	$90.56	$90.55	$90.60
Purchase #2	$94.40	4.463%	$98.6131	$98.61	$98.60	$98.60
Purchase #3	$63.88	4.478%	$66.7405	$66.74	$66.75	$66.70
Purchase #4	$241.60	4.194%	$251.7327	$251.73	$251.75	$251.70
Purchase #5	$173.98	7.640%	$187.2721	$187.27	$187.25	$187.30
Purchase #6	$85.49	8.553%	$92.802	$92.80	$92.80	$92.80
Purchase #7	$194.68	8.830%	$211.8702	$211.87	$211.85	$211.90
7 purchase totals =	$936.59		$999.5907	$999.58	$999.55	$999.60