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	$158.79	12.792%	$179.1024	$179.10	$179.10	$179.10
Purchase #2	$210.65	7.349%	$226.1307	$226.13	$226.15	$226.10
Purchase #3	$145.76	7.213%	$156.2737	$156.27	$156.25	$156.30
Purchase #4	$55.36	13.599%	$62.8884	$62.89	$62.90	$62.90
Purchase #5	$27.96	5.857%	$29.5976	$29.60	$29.60	$29.60
Purchase #6	$131.44	10.419%	$145.1347	$145.13	$145.15	$145.10
Purchase #7	$160.88	6.145%	$170.7661	$170.77	$170.75	$170.80
7 purchase totals =	$890.84		$969.8936	$969.89	$969.90	$969.90