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	$33.53	6.835%	$35.8218	$35.82	$35.80	$35.80
Purchase #2	$153.80	12.169%	$172.5159	$172.52	$172.50	$172.50
Purchase #3	$124.59	5.451%	$131.3814	$131.38	$131.40	$131.40
Purchase #4	$250.31	5.622%	$264.3824	$264.38	$264.40	$264.40
Purchase #5	$105.74	9.639%	$115.9323	$115.93	$115.95	$115.90
Purchase #6	$178.61	8.398%	$193.6097	$193.61	$193.60	$193.60
Purchase #7	$91.46	12.361%	$102.7654	$102.77	$102.75	$102.80
7 purchase totals =	$938.04		$1,016.4089	$1,016.41	$1,016.40	$1,016.40