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	$250.29	9.815%	$274.856	$274.86	$274.85	$274.90
Purchase #2	$74.33	6.271%	$78.9912	$78.99	$79.00	$79.00
Purchase #3	$69.86	12.439%	$78.5499	$78.55	$78.55	$78.50
Purchase #4	$134.62	5.105%	$141.4924	$141.49	$141.50	$141.50
Purchase #5	$237.36	13.151%	$268.5752	$268.58	$268.60	$268.60
Purchase #6	$34.96	5.233%	$36.7895	$36.79	$36.80	$36.80
Purchase #7	$156.43	6.703%	$166.9155	$166.92	$166.90	$166.90
7 purchase totals =	$957.85		$1,046.1697	$1,046.18	$1,046.20	$1,046.20