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	$49.66	9.810%	$54.5316	$54.53	$54.55	$54.50
Purchase #2	$158.43	6.523%	$168.7644	$168.76	$168.75	$168.80
Purchase #3	$62.26	9.505%	$68.1778	$68.18	$68.20	$68.20
Purchase #4	$185.45	5.573%	$195.7851	$195.79	$195.80	$195.80
Purchase #5	$79.54	13.355%	$90.1626	$90.16	$90.15	$90.20
Purchase #6	$110.44	11.406%	$123.0368	$123.04	$123.05	$123.00
Purchase #7	$55.32	3.136%	$57.0548	$57.05	$57.05	$57.10
7 purchase totals =	$701.10		$757.5131	$757.51	$757.55	$757.60