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	$221.43	6.714%	$236.2968	$236.30	$236.30	$236.30
Purchase #2	$74.88	13.717%	$85.1513	$85.15	$85.15	$85.20
Purchase #3	$70.56	11.647%	$78.7781	$78.78	$78.80	$78.80
Purchase #4	$58.54	10.278%	$64.5567	$64.56	$64.55	$64.60
Purchase #5	$68.46	7.496%	$73.5918	$73.59	$73.60	$73.60
Purchase #6	$104.46	5.673%	$110.386	$110.39	$110.40	$110.40
Purchase #7	$14.98	5.820%	$15.8518	$15.85	$15.85	$15.90
7 purchase totals =	$613.31		$664.6125	$664.62	$664.65	$664.80