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	$94.34	5.743%	$99.7579	$99.76	$99.75	$99.80
Purchase #2	$70.42	10.514%	$77.824	$77.82	$77.80	$77.80
Purchase #3	$103.38	6.320%	$109.9136	$109.91	$109.90	$109.90
Purchase #4	$134.40	10.660%	$148.727	$148.73	$148.75	$148.70
Purchase #5	$45.70	7.271%	$49.0228	$49.02	$49.00	$49.00
Purchase #6	$96.64	13.169%	$109.3665	$109.37	$109.35	$109.40
Purchase #7	$223.49	8.402%	$242.2676	$242.27	$242.25	$242.30
7 purchase totals =	$768.37		$836.8794	$836.88	$836.80	$836.90