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	$148.31	13.335%	$168.0871	$168.09	$168.10	$168.10
Purchase #2	$66.34	3.146%	$68.4271	$68.43	$68.45	$68.40
Purchase #3	$233.28	7.533%	$250.853	$250.85	$250.85	$250.90
Purchase #4	$112.50	12.560%	$126.63	$126.63	$126.65	$126.60
Purchase #5	$46.89	3.312%	$48.443	$48.44	$48.45	$48.40
Purchase #6	$55.50	11.158%	$61.6927	$61.69	$61.70	$61.70
Purchase #7	$168.55	4.484%	$176.1078	$176.11	$176.10	$176.10
7 purchase totals =	$831.37		$900.2407	$900.24	$900.30	$900.20