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	$159.68	3.645%	$165.5003	$165.50	$165.50	$165.50
Purchase #2	$39.85	11.427%	$44.4037	$44.40	$44.40	$44.40
Purchase #3	$151.45	9.749%	$166.2149	$166.21	$166.20	$166.20
Purchase #4	$229.44	4.573%	$239.9323	$239.93	$239.95	$239.90
Purchase #5	$225.92	3.743%	$234.3762	$234.38	$234.40	$234.40
Purchase #6	$78.94	4.510%	$82.5002	$82.50	$82.50	$82.50
Purchase #7	$64.39	12.532%	$72.4594	$72.46	$72.45	$72.50
7 purchase totals =	$949.67		$1,005.3870	$1,005.38	$1,005.40	$1,005.40