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	$225.57	10.529%	$249.3203	$249.32	$249.30	$249.30
Purchase #2	$38.88	8.164%	$42.0542	$42.05	$42.05	$42.10
Purchase #3	$154.79	6.650%	$165.0835	$165.08	$165.10	$165.10
Purchase #4	$132.30	9.396%	$144.7309	$144.73	$144.75	$144.70
Purchase #5	$232.81	12.501%	$261.9136	$261.91	$261.90	$261.90
Purchase #6	$42.55	6.486%	$45.3098	$45.31	$45.30	$45.30
Purchase #7	$142.35	13.839%	$162.0498	$162.05	$162.05	$162.00
7 purchase totals =	$969.25		$1,070.4621	$1,070.45	$1,070.45	$1,070.40