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	$98.44	10.578%	$108.853	$108.85	$108.85	$108.90
Purchase #2	$112.86	13.383%	$127.9641	$127.96	$127.95	$128.00
Purchase #3	$46.32	5.519%	$48.8764	$48.88	$48.90	$48.90
Purchase #4	$123.98	8.139%	$134.0707	$134.07	$134.05	$134.10
Purchase #5	$28.35	9.303%	$30.9874	$30.99	$31.00	$31.00
Purchase #6	$6.78	4.299%	$7.0715	$7.07	$7.05	$7.10
Purchase #7	$92.86	8.627%	$100.871	$100.87	$100.85	$100.90
7 purchase totals =	$509.59		$558.6941	$558.69	$558.65	$558.90