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	$170.33	9.720%	$186.8861	$186.89	$186.90	$186.90
Purchase #2	$127.90	13.672%	$145.3865	$145.39	$145.40	$145.40
Purchase #3	$79.43	13.303%	$89.9966	$90.00	$90.00	$90.00
Purchase #4	$48.58	9.752%	$53.3175	$53.32	$53.30	$53.30
Purchase #5	$77.53	11.396%	$86.3653	$86.37	$86.35	$86.40
Purchase #6	$71.64	7.595%	$77.0811	$77.08	$77.10	$77.10
Purchase #7	$180.54	3.857%	$187.5034	$187.50	$187.50	$187.50
7 purchase totals =	$755.95		$826.5365	$826.55	$826.55	$826.60