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	$105.65	10.282%	$116.5129	$116.51	$116.50	$116.50
Purchase #2	$97.93	7.782%	$105.5509	$105.55	$105.55	$105.60
Purchase #3	$218.96	10.734%	$242.4632	$242.46	$242.45	$242.50
Purchase #4	$96.51	4.120%	$100.4862	$100.49	$100.50	$100.50
Purchase #5	$232.51	10.225%	$256.2841	$256.28	$256.30	$256.30
Purchase #6	$197.49	6.646%	$210.6152	$210.62	$210.60	$210.60
Purchase #7	$241.33	7.178%	$258.6527	$258.65	$258.65	$258.70
7 purchase totals =	$1,190.38		$1,290.5652	$1,290.56	$1,290.55	$1,290.70