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	$148.54	5.384%	$156.5374	$156.54	$156.55	$156.50
Purchase #2	$231.80	7.519%	$249.229	$249.23	$249.25	$249.20
Purchase #3	$36.31	8.586%	$39.4276	$39.43	$39.45	$39.40
Purchase #4	$21.69	11.287%	$24.1382	$24.14	$24.15	$24.10
Purchase #5	$57.39	10.657%	$63.5061	$63.51	$63.50	$63.50
Purchase #6	$129.78	9.820%	$142.5244	$142.52	$142.50	$142.50
Purchase #7	$127.76	5.278%	$134.5032	$134.50	$134.50	$134.50
7 purchase totals =	$753.27		$809.8659	$809.87	$809.90	$809.70