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	$78.88	13.413%	$89.4602	$89.46	$89.45	$89.50
Purchase #2	$41.76	7.424%	$44.8603	$44.86	$44.85	$44.90
Purchase #3	$72.72	6.823%	$77.6817	$77.68	$77.70	$77.70
Purchase #4	$122.42	4.321%	$127.7098	$127.71	$127.70	$127.70
Purchase #5	$85.81	11.671%	$95.8249	$95.82	$95.80	$95.80
Purchase #6	$241.90	9.444%	$264.745	$264.75	$264.75	$264.70
Purchase #7	$86.95	9.618%	$95.3129	$95.31	$95.30	$95.30
7 purchase totals =	$730.44		$795.5948	$795.59	$795.55	$795.60