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	$17.95	4.599%	$18.7755	$18.78	$18.80	$18.80
Purchase #2	$70.40	3.183%	$72.6408	$72.64	$72.65	$72.60
Purchase #3	$150.28	10.354%	$165.84	$165.84	$165.85	$165.80
Purchase #4	$164.29	9.146%	$179.316	$179.32	$179.30	$179.30
Purchase #5	$71.93	3.478%	$74.4317	$74.43	$74.45	$74.40
Purchase #6	$40.53	7.238%	$43.4636	$43.46	$43.45	$43.50
Purchase #7	$63.54	4.290%	$66.2659	$66.27	$66.25	$66.30
7 purchase totals =	$578.92		$620.7335	$620.74	$620.75	$620.70