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	$47.34	10.549%	$52.3339	$52.33	$52.35	$52.30
Purchase #2	$49.39	7.331%	$53.0108	$53.01	$53.00	$53.00
Purchase #3	$40.25	13.369%	$45.631	$45.63	$45.65	$45.60
Purchase #4	$226.80	5.151%	$238.4825	$238.48	$238.50	$238.50
Purchase #5	$138.83	3.607%	$143.8376	$143.84	$143.85	$143.80
Purchase #6	$137.85	4.123%	$143.5336	$143.53	$143.55	$143.50
Purchase #7	$114.99	9.841%	$126.3062	$126.31	$126.30	$126.30
7 purchase totals =	$755.45		$803.1356	$803.13	$803.20	$803.00