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	$114.52	11.267%	$127.423	$127.42	$127.40	$127.40
Purchase #2	$42.66	5.743%	$45.11	$45.11	$45.10	$45.10
Purchase #3	$92.84	7.691%	$99.9803	$99.98	$100.00	$100.00
Purchase #4	$118.83	4.132%	$123.7401	$123.74	$123.75	$123.70
Purchase #5	$59.47	4.783%	$62.3145	$62.31	$62.30	$62.30
Purchase #6	$83.27	10.566%	$92.0683	$92.07	$92.05	$92.10
Purchase #7	$125.56	10.408%	$138.6283	$138.63	$138.65	$138.60
7 purchase totals =	$637.15		$689.2645	$689.26	$689.25	$689.20