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	$240.43	12.478%	$270.4309	$270.43	$270.45	$270.40
Purchase #2	$90.26	6.498%	$96.1251	$96.13	$96.15	$96.10
Purchase #3	$169.48	9.348%	$185.323	$185.32	$185.30	$185.30
Purchase #4	$148.37	11.357%	$165.2204	$165.22	$165.20	$165.20
Purchase #5	$199.74	13.874%	$227.4519	$227.45	$227.45	$227.50
Purchase #6	$138.98	3.641%	$144.0403	$144.04	$144.05	$144.00
Purchase #7	$146.40	5.486%	$154.4315	$154.43	$154.45	$154.40
7 purchase totals =	$1,133.66		$1,243.0231	$1,243.02	$1,243.05	$1,242.90