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	$109.65	12.610%	$123.4769	$123.48	$123.50	$123.50
Purchase #2	$130.30	6.468%	$138.7278	$138.73	$138.75	$138.70
Purchase #3	$110.34	5.537%	$116.4495	$116.45	$116.45	$116.40
Purchase #4	$142.30	5.812%	$150.5705	$150.57	$150.55	$150.60
Purchase #5	$95.34	5.186%	$100.2843	$100.28	$100.30	$100.30
Purchase #6	$29.32	5.119%	$30.8209	$30.82	$30.80	$30.80
Purchase #7	$93.65	8.353%	$101.4726	$101.47	$101.45	$101.50
7 purchase totals =	$710.90		$761.8025	$761.80	$761.80	$761.80