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	$151.79	13.663%	$172.5291	$172.53	$172.55	$172.50
Purchase #2	$95.28	10.837%	$105.6055	$105.61	$105.60	$105.60
Purchase #3	$47.78	5.780%	$50.5417	$50.54	$50.55	$50.50
Purchase #4	$175.63	10.185%	$193.5179	$193.52	$193.50	$193.50
Purchase #5	$51.72	6.144%	$54.8977	$54.90	$54.90	$54.90
Purchase #6	$101.63	12.543%	$114.3775	$114.38	$114.40	$114.40
Purchase #7	$240.89	3.111%	$248.3841	$248.38	$248.40	$248.40
7 purchase totals =	$864.72		$939.8535	$939.86	$939.90	$939.80