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	$63.40	13.389%	$71.8886	$71.89	$71.90	$71.90
Purchase #2	$172.51	8.670%	$187.4666	$187.47	$187.45	$187.50
Purchase #3	$51.44	7.508%	$55.3021	$55.30	$55.30	$55.30
Purchase #4	$80.55	12.132%	$90.3223	$90.32	$90.30	$90.30
Purchase #5	$117.76	11.388%	$131.1705	$131.17	$131.15	$131.20
Purchase #6	$149.97	3.478%	$155.186	$155.19	$155.20	$155.20
Purchase #7	$155.89	9.453%	$170.6263	$170.63	$170.65	$170.60
7 purchase totals =	$791.52		$861.9624	$861.97	$861.95	$862.00