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	$85.63	5.172%	$90.0588	$90.06	$90.05	$90.10
Purchase #2	$172.28	5.300%	$181.4108	$181.41	$181.40	$181.40
Purchase #3	$140.81	12.321%	$158.1592	$158.16	$158.15	$158.20
Purchase #4	$95.50	6.758%	$101.9539	$101.95	$101.95	$102.00
Purchase #5	$136.78	7.289%	$146.7499	$146.75	$146.75	$146.70
Purchase #6	$71.57	13.731%	$81.3973	$81.40	$81.40	$81.40
Purchase #7	$33.90	8.546%	$36.7971	$36.80	$36.80	$36.80
7 purchase totals =	$736.47		$796.5270	$796.53	$796.50	$796.60