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	$96.75	3.391%	$100.0308	$100.03	$100.05	$100.00
Purchase #2	$129.48	5.167%	$136.1702	$136.17	$136.15	$136.20
Purchase #3	$82.30	9.406%	$90.0411	$90.04	$90.05	$90.00
Purchase #4	$90.63	10.284%	$99.9504	$99.95	$99.95	$100.00
Purchase #5	$150.31	8.396%	$162.93	$162.93	$162.95	$162.90
Purchase #6	$146.98	10.480%	$162.3835	$162.38	$162.40	$162.40
Purchase #7	$14.64	6.427%	$15.5809	$15.58	$15.60	$15.60
7 purchase totals =	$711.09		$767.0869	$767.08	$767.15	$767.10