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	$33.40	13.403%	$37.8766	$37.88	$37.90	$37.90
Purchase #2	$212.88	11.586%	$237.5443	$237.54	$237.55	$237.50
Purchase #3	$83.76	3.267%	$86.4964	$86.50	$86.50	$86.50
Purchase #4	$195.52	6.692%	$208.6042	$208.60	$208.60	$208.60
Purchase #5	$129.86	3.525%	$134.4376	$134.44	$134.45	$134.40
Purchase #6	$85.27	10.736%	$94.4246	$94.42	$94.40	$94.40
Purchase #7	$84.78	7.653%	$91.2682	$91.27	$91.25	$91.30
7 purchase totals =	$825.47		$890.6519	$890.65	$890.65	$890.60