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	$33.43	5.702%	$35.3362	$35.34	$35.35	$35.30
Purchase #2	$137.45	12.651%	$154.8388	$154.84	$154.85	$154.80
Purchase #3	$95.83	4.793%	$100.4231	$100.42	$100.40	$100.40
Purchase #4	$203.39	9.711%	$223.1412	$223.14	$223.15	$223.10
Purchase #5	$231.51	8.641%	$251.5148	$251.51	$251.50	$251.50
Purchase #6	$140.74	6.680%	$150.1414	$150.14	$150.15	$150.10
Purchase #7	$21.65	11.153%	$24.0646	$24.06	$24.05	$24.10
7 purchase totals =	$864.00		$939.4601	$939.45	$939.45	$939.30