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	$103.41	12.498%	$116.3342	$116.33	$116.35	$116.30
Purchase #2	$60.86	7.410%	$65.3697	$65.37	$65.35	$65.40
Purchase #3	$197.57	5.847%	$209.1219	$209.12	$209.10	$209.10
Purchase #4	$59.41	4.163%	$61.8832	$61.88	$61.90	$61.90
Purchase #5	$153.89	6.559%	$163.9836	$163.98	$164.00	$164.00
Purchase #6	$131.60	5.740%	$139.1538	$139.15	$139.15	$139.20
Purchase #7	$12.54	8.668%	$13.627	$13.63	$13.65	$13.60
7 purchase totals =	$719.28		$769.4734	$769.46	$769.50	$769.50