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	$126.39	6.628%	$134.7671	$134.77	$134.75	$134.80
Purchase #2	$249.36	12.649%	$280.9015	$280.90	$280.90	$280.90
Purchase #3	$94.96	5.417%	$100.104	$100.10	$100.10	$100.10
Purchase #4	$158.79	4.614%	$166.1166	$166.12	$166.10	$166.10
Purchase #5	$32.90	3.225%	$33.961	$33.96	$33.95	$34.00
Purchase #6	$49.63	6.659%	$52.9349	$52.93	$52.95	$52.90
Purchase #7	$25.51	11.645%	$28.4806	$28.48	$28.50	$28.50
7 purchase totals =	$737.54		$797.2657	$797.26	$797.25	$797.30