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	$110.97	5.226%	$116.7693	$116.77	$116.75	$116.80
Purchase #2	$19.72	10.737%	$21.8373	$21.84	$21.85	$21.80
Purchase #3	$214.31	11.345%	$238.6235	$238.62	$238.60	$238.60
Purchase #4	$120.48	6.112%	$127.8437	$127.84	$127.85	$127.80
Purchase #5	$109.59	7.606%	$117.9254	$117.93	$117.95	$117.90
Purchase #6	$96.87	5.416%	$102.1165	$102.12	$102.10	$102.10
Purchase #7	$31.95	9.655%	$35.0348	$35.03	$35.05	$35.00
7 purchase totals =	$703.89		$760.1505	$760.15	$760.15	$760.00