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	$165.56	12.522%	$186.2914	$186.29	$186.30	$186.30
Purchase #2	$39.86	12.545%	$44.8604	$44.86	$44.85	$44.90
Purchase #3	$116.33	9.550%	$127.4395	$127.44	$127.45	$127.40
Purchase #4	$130.93	12.198%	$146.9008	$146.90	$146.90	$146.90
Purchase #5	$210.61	5.792%	$222.8085	$222.81	$222.80	$222.80
Purchase #6	$28.68	13.363%	$32.5125	$32.51	$32.50	$32.50
Purchase #7	$84.91	10.731%	$94.0217	$94.02	$94.00	$94.00
7 purchase totals =	$776.88		$854.8348	$854.83	$854.80	$854.80