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	$7.41	8.180%	$8.0161	$8.02	$8.00	$8.00
Purchase #2	$111.82	5.639%	$118.1255	$118.13	$118.15	$118.10
Purchase #3	$57.72	4.366%	$60.2401	$60.24	$60.25	$60.20
Purchase #4	$154.35	5.484%	$162.8146	$162.81	$162.80	$162.80
Purchase #5	$147.80	13.370%	$167.5609	$167.56	$167.55	$167.60
Purchase #6	$62.48	12.779%	$70.4643	$70.46	$70.45	$70.50
Purchase #7	$99.36	6.274%	$105.5938	$105.59	$105.60	$105.60
7 purchase totals =	$640.94		$692.8153	$692.81	$692.80	$692.80