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	$36.40	9.333%	$39.7972	$39.80	$39.80	$39.80
Purchase #2	$83.38	10.246%	$91.9231	$91.92	$91.90	$91.90
Purchase #3	$46.54	8.624%	$50.5536	$50.55	$50.55	$50.60
Purchase #4	$230.33	11.333%	$256.4333	$256.43	$256.45	$256.40
Purchase #5	$228.40	7.324%	$245.128	$245.13	$245.15	$245.10
Purchase #6	$162.97	10.624%	$180.2839	$180.28	$180.30	$180.30
Purchase #7	$214.31	10.162%	$236.0882	$236.09	$236.10	$236.10
7 purchase totals =	$1,002.33		$1,100.2073	$1,100.20	$1,100.25	$1,100.20