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	$106.58	5.524%	$112.4675	$112.47	$112.45	$112.50
Purchase #2	$42.88	12.141%	$48.0861	$48.09	$48.10	$48.10
Purchase #3	$176.83	10.122%	$194.7287	$194.73	$194.75	$194.70
Purchase #4	$122.84	3.513%	$127.1554	$127.16	$127.15	$127.20
Purchase #5	$64.43	13.769%	$73.3014	$73.30	$73.30	$73.30
Purchase #6	$50.57	9.344%	$55.2953	$55.30	$55.30	$55.30
Purchase #7	$162.55	5.401%	$171.3293	$171.33	$171.35	$171.30
7 purchase totals =	$726.68		$782.3637	$782.38	$782.40	$782.40