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	$36.45	6.353%	$38.7657	$38.77	$38.75	$38.80
Purchase #2	$68.78	13.534%	$78.0887	$78.09	$78.10	$78.10
Purchase #3	$93.69	6.360%	$99.6487	$99.65	$99.65	$99.60
Purchase #4	$81.86	9.206%	$89.396	$89.40	$89.40	$89.40
Purchase #5	$68.62	7.666%	$73.8804	$73.88	$73.90	$73.90
Purchase #6	$125.48	5.309%	$132.1417	$132.14	$132.15	$132.10
Purchase #7	$78.64	3.114%	$81.0888	$81.09	$81.10	$81.10
7 purchase totals =	$553.52		$593.0100	$593.02	$593.05	$593.00