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	$236.71	8.243%	$256.222	$256.22	$256.20	$256.20
Purchase #2	$206.81	7.846%	$223.0363	$223.04	$223.05	$223.00
Purchase #3	$58.51	12.801%	$65.9999	$66.00	$66.00	$66.00
Purchase #4	$167.32	12.524%	$188.2752	$188.28	$188.30	$188.30
Purchase #5	$178.30	5.103%	$187.3986	$187.40	$187.40	$187.40
Purchase #6	$71.64	9.309%	$78.309	$78.31	$78.30	$78.30
Purchase #7	$6.37	10.202%	$7.0199	$7.02	$7.00	$7.00
7 purchase totals =	$925.66		$1,006.2609	$1,006.27	$1,006.25	$1,006.20