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	$99.72	11.782%	$111.469	$111.47	$111.45	$111.50
Purchase #2	$110.58	11.262%	$123.0335	$123.03	$123.05	$123.00
Purchase #3	$28.89	12.529%	$32.5096	$32.51	$32.50	$32.50
Purchase #4	$46.33	11.502%	$51.6589	$51.66	$51.65	$51.70
Purchase #5	$69.51	11.797%	$77.7101	$77.71	$77.70	$77.70
Purchase #6	$113.51	4.788%	$118.9449	$118.94	$118.95	$118.90
Purchase #7	$156.64	6.607%	$166.9892	$166.99	$167.00	$167.00
7 purchase totals =	$625.18		$682.3152	$682.31	$682.30	$682.30