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	$122.79	13.392%	$139.234	$139.23	$139.25	$139.20
Purchase #2	$16.39	4.102%	$17.0623	$17.06	$17.05	$17.10
Purchase #3	$202.63	13.791%	$230.5747	$230.57	$230.55	$230.60
Purchase #4	$242.63	5.345%	$255.5986	$255.60	$255.60	$255.60
Purchase #5	$52.59	13.659%	$59.7733	$59.77	$59.75	$59.80
Purchase #6	$34.52	7.514%	$37.1138	$37.11	$37.10	$37.10
Purchase #7	$95.59	11.535%	$106.6163	$106.62	$106.60	$106.60
7 purchase totals =	$767.14		$845.9730	$845.96	$845.90	$846.00