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	$234.87	4.180%	$244.6876	$244.69	$244.70	$244.70
Purchase #2	$39.72	12.391%	$44.6417	$44.64	$44.65	$44.60
Purchase #3	$137.48	9.491%	$150.5282	$150.53	$150.55	$150.50
Purchase #4	$111.64	11.269%	$124.2207	$124.22	$124.20	$124.20
Purchase #5	$188.66	4.143%	$196.4762	$196.48	$196.50	$196.50
Purchase #6	$33.36	10.336%	$36.8081	$36.81	$36.80	$36.80
Purchase #7	$118.48	8.237%	$128.2392	$128.24	$128.25	$128.20
7 purchase totals =	$864.21		$925.6017	$925.61	$925.65	$925.50