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	$108.51	12.184%	$121.7309	$121.73	$121.75	$121.70
Purchase #2	$77.79	5.815%	$82.3135	$82.31	$82.30	$82.30
Purchase #3	$6.95	5.839%	$7.3558	$7.36	$7.35	$7.40
Purchase #4	$124.62	4.178%	$129.8266	$129.83	$129.85	$129.80
Purchase #5	$13.69	13.234%	$15.5017	$15.50	$15.50	$15.50
Purchase #6	$86.86	3.487%	$89.8888	$89.89	$89.90	$89.90
Purchase #7	$81.67	10.200%	$90.0003	$90.00	$90.00	$90.00
7 purchase totals =	$500.09		$536.6176	$536.62	$536.65	$536.60