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	$101.64	6.806%	$108.5576	$108.56	$108.55	$108.60
Purchase #2	$82.41	10.413%	$90.9914	$90.99	$91.00	$91.00
Purchase #3	$136.78	11.751%	$152.853	$152.85	$152.85	$152.90
Purchase #4	$22.90	11.702%	$25.5798	$25.58	$25.60	$25.60
Purchase #5	$72.32	7.248%	$77.5618	$77.56	$77.55	$77.60
Purchase #6	$109.76	13.551%	$124.6336	$124.63	$124.65	$124.60
Purchase #7	$196.65	4.152%	$204.8149	$204.81	$204.80	$204.80
7 purchase totals =	$722.46		$784.9921	$784.98	$785.00	$785.10