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	$35.29	12.835%	$39.8195	$39.82	$39.80	$39.80
Purchase #2	$28.36	11.348%	$31.5783	$31.58	$31.60	$31.60
Purchase #3	$54.40	5.615%	$57.4546	$57.45	$57.45	$57.50
Purchase #4	$24.39	4.813%	$25.5639	$25.56	$25.55	$25.60
Purchase #5	$67.88	13.499%	$77.0431	$77.04	$77.05	$77.00
Purchase #6	$65.78	13.443%	$74.6228	$74.62	$74.60	$74.60
Purchase #7	$55.64	10.272%	$61.3553	$61.36	$61.35	$61.40
7 purchase totals =	$331.74		$367.4375	$367.43	$367.40	$367.50