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	$137.49	9.626%	$150.7248	$150.72	$150.70	$150.70
Purchase #2	$46.47	11.298%	$51.7202	$51.72	$51.70	$51.70
Purchase #3	$79.93	11.215%	$88.8941	$88.89	$88.90	$88.90
Purchase #4	$129.71	7.240%	$139.101	$139.10	$139.10	$139.10
Purchase #5	$9.62	3.782%	$9.9838	$9.98	$10.00	$10.00
Purchase #6	$68.98	12.578%	$77.6563	$77.66	$77.65	$77.70
Purchase #7	$116.78	5.453%	$123.148	$123.15	$123.15	$123.10
7 purchase totals =	$588.98		$641.2282	$641.22	$641.20	$641.20