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	$105.91	7.218%	$113.5546	$113.55	$113.55	$113.60
Purchase #2	$49.60	6.616%	$52.8815	$52.88	$52.90	$52.90
Purchase #3	$90.40	12.278%	$101.4993	$101.50	$101.50	$101.50
Purchase #4	$78.58	13.421%	$89.1262	$89.13	$89.15	$89.10
Purchase #5	$26.86	9.390%	$29.3822	$29.38	$29.40	$29.40
Purchase #6	$183.73	10.111%	$202.3069	$202.31	$202.30	$202.30
Purchase #7	$214.96	7.795%	$231.7161	$231.72	$231.70	$231.70
7 purchase totals =	$750.04		$820.4668	$820.47	$820.50	$820.50