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	$223.98	13.181%	$253.5028	$253.50	$253.50	$253.50
Purchase #2	$249.54	10.670%	$276.1659	$276.17	$276.15	$276.20
Purchase #3	$129.72	11.691%	$144.8856	$144.89	$144.90	$144.90
Purchase #4	$82.25	9.446%	$90.0193	$90.02	$90.00	$90.00
Purchase #5	$69.82	5.526%	$73.6783	$73.68	$73.70	$73.70
Purchase #6	$162.63	9.819%	$178.5986	$178.60	$178.60	$178.60
Purchase #7	$111.99	12.836%	$126.365	$126.37	$126.35	$126.40
7 purchase totals =	$1,029.93		$1,143.2155	$1,143.23	$1,143.20	$1,143.30