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	$48.58	12.466%	$54.636	$54.64	$54.65	$54.60
Purchase #2	$61.80	5.524%	$65.2138	$65.21	$65.20	$65.20
Purchase #3	$98.42	10.789%	$109.0385	$109.04	$109.05	$109.00
Purchase #4	$65.27	10.476%	$72.1077	$72.11	$72.10	$72.10
Purchase #5	$142.89	7.295%	$153.3138	$153.31	$153.30	$153.30
Purchase #6	$90.58	3.751%	$93.9777	$93.98	$94.00	$94.00
Purchase #7	$104.97	13.261%	$118.8901	$118.89	$118.90	$118.90
7 purchase totals =	$612.51		$667.1776	$667.18	$667.20	$667.10