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	$57.40	3.810%	$59.5869	$59.59	$59.60	$59.60
Purchase #2	$199.27	10.304%	$219.8028	$219.80	$219.80	$219.80
Purchase #3	$222.47	5.224%	$234.0918	$234.09	$234.10	$234.10
Purchase #4	$60.32	4.728%	$63.1719	$63.17	$63.15	$63.20
Purchase #5	$155.75	5.586%	$164.4502	$164.45	$164.45	$164.50
Purchase #6	$87.76	11.557%	$97.9024	$97.90	$97.90	$97.90
Purchase #7	$103.31	11.112%	$114.7898	$114.79	$114.80	$114.80
7 purchase totals =	$886.28		$953.7958	$953.79	$953.80	$953.90