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	$135.51	9.453%	$148.3198	$148.32	$148.30	$148.30
Purchase #2	$243.40	5.257%	$256.1955	$256.20	$256.20	$256.20
Purchase #3	$112.53	11.631%	$125.6184	$125.62	$125.60	$125.60
Purchase #4	$123.42	13.538%	$140.1286	$140.13	$140.15	$140.10
Purchase #5	$225.90	9.132%	$246.5292	$246.53	$246.55	$246.50
Purchase #6	$37.63	9.197%	$41.0908	$41.09	$41.10	$41.10
Purchase #7	$100.28	11.570%	$111.8824	$111.88	$111.90	$111.90
7 purchase totals =	$978.67		$1,069.7647	$1,069.77	$1,069.80	$1,069.70