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	$84.87	6.147%	$90.087	$90.09	$90.10	$90.10
Purchase #2	$183.84	6.534%	$195.8521	$195.85	$195.85	$195.90
Purchase #3	$137.69	5.685%	$145.5177	$145.52	$145.50	$145.50
Purchase #4	$86.71	3.796%	$90.0015	$90.00	$90.00	$90.00
Purchase #5	$124.50	11.441%	$138.744	$138.74	$138.75	$138.70
Purchase #6	$190.62	11.384%	$212.3202	$212.32	$212.30	$212.30
Purchase #7	$179.26	5.161%	$188.5116	$188.51	$188.50	$188.50
7 purchase totals =	$987.49		$1,061.0341	$1,061.03	$1,061.00	$1,061.00