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	$95.29	8.170%	$103.0752	$103.08	$103.10	$103.10
Purchase #2	$166.53	13.154%	$188.4354	$188.44	$188.45	$188.40
Purchase #3	$141.36	10.532%	$156.248	$156.25	$156.25	$156.20
Purchase #4	$89.35	13.791%	$101.6723	$101.67	$101.65	$101.70
Purchase #5	$70.31	3.110%	$72.4966	$72.50	$72.50	$72.50
Purchase #6	$128.96	10.334%	$142.2867	$142.29	$142.30	$142.30
Purchase #7	$206.93	5.157%	$217.6014	$217.60	$217.60	$217.60
7 purchase totals =	$898.73		$981.8156	$981.83	$981.85	$981.80