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	$73.45	11.845%	$82.1502	$82.15	$82.15	$82.20
Purchase #2	$222.40	9.291%	$243.0632	$243.06	$243.05	$243.10
Purchase #3	$232.78	13.857%	$265.0363	$265.04	$265.05	$265.00
Purchase #4	$113.34	3.684%	$117.5154	$117.52	$117.50	$117.50
Purchase #5	$133.98	10.682%	$148.2917	$148.29	$148.30	$148.30
Purchase #6	$198.42	10.450%	$219.1549	$219.15	$219.15	$219.20
Purchase #7	$42.27	7.371%	$45.3857	$45.39	$45.40	$45.40
7 purchase totals =	$1,016.64		$1,120.5974	$1,120.60	$1,120.60	$1,120.70