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	$43.92	12.289%	$49.3173	$49.32	$49.30	$49.30
Purchase #2	$144.40	6.489%	$153.7701	$153.77	$153.75	$153.80
Purchase #3	$72.64	4.755%	$76.094	$76.09	$76.10	$76.10
Purchase #4	$96.26	13.396%	$109.155	$109.16	$109.15	$109.20
Purchase #5	$81.57	4.538%	$85.2716	$85.27	$85.25	$85.30
Purchase #6	$55.82	9.242%	$60.9789	$60.98	$61.00	$61.00
Purchase #7	$44.85	12.836%	$50.6069	$50.61	$50.60	$50.60
7 purchase totals =	$539.46		$585.1938	$585.20	$585.15	$585.30