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	$112.33	13.472%	$127.4631	$127.46	$127.45	$127.50
Purchase #2	$155.42	3.375%	$160.6654	$160.67	$160.65	$160.70
Purchase #3	$208.86	11.697%	$233.2904	$233.29	$233.30	$233.30
Purchase #4	$87.67	11.137%	$97.4338	$97.43	$97.45	$97.40
Purchase #5	$92.36	6.691%	$98.5398	$98.54	$98.55	$98.50
Purchase #6	$109.40	8.327%	$118.5097	$118.51	$118.50	$118.50
Purchase #7	$62.56	3.304%	$64.627	$64.63	$64.65	$64.60
7 purchase totals =	$828.60		$900.5292	$900.53	$900.55	$900.50