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	$108.41	9.141%	$118.3198	$118.32	$118.30	$118.30
Purchase #2	$151.25	4.320%	$157.784	$157.78	$157.80	$157.80
Purchase #3	$74.31	6.242%	$78.9484	$78.95	$78.95	$78.90
Purchase #4	$218.89	4.681%	$229.1362	$229.14	$229.15	$229.10
Purchase #5	$152.73	9.158%	$166.717	$166.72	$166.70	$166.70
Purchase #6	$159.60	7.405%	$171.4184	$171.42	$171.40	$171.40
Purchase #7	$51.83	5.817%	$54.845	$54.85	$54.85	$54.80
7 purchase totals =	$917.02		$977.1688	$977.18	$977.15	$977.00