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	$248.43	11.335%	$276.5895	$276.59	$276.60	$276.60
Purchase #2	$174.49	13.385%	$197.8455	$197.85	$197.85	$197.80
Purchase #3	$64.55	11.309%	$71.85	$71.85	$71.85	$71.90
Purchase #4	$106.43	7.607%	$114.5261	$114.53	$114.55	$114.50
Purchase #5	$66.66	8.330%	$72.2128	$72.21	$72.20	$72.20
Purchase #6	$78.92	13.816%	$89.8236	$89.82	$89.80	$89.80
Purchase #7	$21.80	5.227%	$22.9395	$22.94	$22.95	$22.90
7 purchase totals =	$761.28		$845.7870	$845.79	$845.80	$845.70