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	$242.80	10.224%	$267.6239	$267.62	$267.60	$267.60
Purchase #2	$190.69	9.842%	$209.4577	$209.46	$209.45	$209.50
Purchase #3	$29.47	3.643%	$30.5436	$30.54	$30.55	$30.50
Purchase #4	$53.45	11.827%	$59.7715	$59.77	$59.75	$59.80
Purchase #5	$36.45	12.791%	$41.1123	$41.11	$41.10	$41.10
Purchase #6	$91.35	10.583%	$101.0176	$101.02	$101.00	$101.00
Purchase #7	$90.68	9.808%	$99.5739	$99.57	$99.55	$99.60
7 purchase totals =	$734.89		$809.1005	$809.09	$809.00	$809.10