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	$89.97	11.407%	$100.2329	$100.23	$100.25	$100.20
Purchase #2	$89.59	11.800%	$100.1616	$100.16	$100.15	$100.20
Purchase #3	$174.71	10.130%	$192.4081	$192.41	$192.40	$192.40
Purchase #4	$85.98	8.456%	$93.2505	$93.25	$93.25	$93.30
Purchase #5	$79.41	4.825%	$83.2415	$83.24	$83.25	$83.20
Purchase #6	$72.28	7.495%	$77.6974	$77.70	$77.70	$77.70
Purchase #7	$74.83	8.665%	$81.314	$81.31	$81.30	$81.30
7 purchase totals =	$666.77		$728.3060	$728.30	$728.30	$728.30