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	$17.25	9.529%	$18.8938	$18.89	$18.90	$18.90
Purchase #2	$42.43	3.608%	$43.9609	$43.96	$43.95	$44.00
Purchase #3	$34.89	4.221%	$36.3627	$36.36	$36.35	$36.40
Purchase #4	$39.39	11.447%	$43.899	$43.90	$43.90	$43.90
Purchase #5	$176.35	6.795%	$188.333	$188.33	$188.35	$188.30
Purchase #6	$82.41	13.467%	$93.5082	$93.51	$93.50	$93.50
Purchase #7	$123.42	7.448%	$132.6123	$132.61	$132.60	$132.60
7 purchase totals =	$516.14		$557.5699	$557.56	$557.55	$557.60