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	$166.58	9.199%	$181.9037	$181.90	$181.90	$181.90
Purchase #2	$97.91	7.161%	$104.9213	$104.92	$104.90	$104.90
Purchase #3	$40.37	7.138%	$43.2516	$43.25	$43.25	$43.30
Purchase #4	$186.36	7.824%	$200.9408	$200.94	$200.95	$200.90
Purchase #5	$35.98	10.523%	$39.7662	$39.77	$39.75	$39.80
Purchase #6	$40.27	6.408%	$42.8505	$42.85	$42.85	$42.90
Purchase #7	$247.70	11.667%	$276.5992	$276.60	$276.60	$276.60
7 purchase totals =	$815.17		$890.2333	$890.23	$890.20	$890.30