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	$83.50	7.682%	$89.9145	$89.91	$89.90	$89.90
Purchase #2	$235.95	13.707%	$268.2917	$268.29	$268.30	$268.30
Purchase #3	$173.87	12.523%	$195.6437	$195.64	$195.65	$195.60
Purchase #4	$188.43	3.124%	$194.3166	$194.32	$194.30	$194.30
Purchase #5	$98.98	6.538%	$105.4513	$105.45	$105.45	$105.50
Purchase #6	$132.71	8.822%	$144.4177	$144.42	$144.40	$144.40
Purchase #7	$157.86	6.481%	$168.0909	$168.09	$168.10	$168.10
7 purchase totals =	$1,071.30		$1,166.1264	$1,166.12	$1,166.10	$1,166.10