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	$74.34	7.652%	$80.0285	$80.03	$80.05	$80.00
Purchase #2	$127.63	10.866%	$141.4983	$141.50	$141.50	$141.50
Purchase #3	$151.99	5.853%	$160.886	$160.89	$160.90	$160.90
Purchase #4	$110.89	13.871%	$126.2716	$126.27	$126.25	$126.30
Purchase #5	$136.70	6.624%	$145.755	$145.76	$145.75	$145.80
Purchase #6	$79.40	8.227%	$85.9322	$85.93	$85.95	$85.90
Purchase #7	$96.64	9.289%	$105.6169	$105.62	$105.60	$105.60
7 purchase totals =	$777.59		$845.9885	$846.00	$846.00	$846.00