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	$31.59	5.418%	$33.3015	$33.30	$33.30	$33.30
Purchase #2	$144.99	8.227%	$156.9183	$156.92	$156.90	$156.90
Purchase #3	$239.86	10.699%	$265.5226	$265.52	$265.50	$265.50
Purchase #4	$93.93	5.371%	$98.975	$98.98	$99.00	$99.00
Purchase #5	$132.31	5.411%	$139.4693	$139.47	$139.45	$139.50
Purchase #6	$132.91	3.332%	$137.3386	$137.34	$137.35	$137.30
Purchase #7	$232.50	9.274%	$254.0621	$254.06	$254.05	$254.10
7 purchase totals =	$1,008.09		$1,085.5874	$1,085.59	$1,085.55	$1,085.60