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	$142.52	6.365%	$151.5914	$151.59	$151.60	$151.60
Purchase #2	$230.30	13.432%	$261.2339	$261.23	$261.25	$261.20
Purchase #3	$79.40	7.347%	$85.2335	$85.23	$85.25	$85.20
Purchase #4	$114.56	13.457%	$129.9763	$129.98	$130.00	$130.00
Purchase #5	$82.77	12.223%	$92.887	$92.89	$92.90	$92.90
Purchase #6	$63.30	5.260%	$66.6296	$66.63	$66.65	$66.60
Purchase #7	$61.81	5.440%	$65.1725	$65.17	$65.15	$65.20
7 purchase totals =	$774.66		$852.7242	$852.72	$852.80	$852.70