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	$51.43	10.608%	$56.8857	$56.89	$56.90	$56.90
Purchase #2	$6.74	10.249%	$7.4308	$7.43	$7.45	$7.40
Purchase #3	$43.35	5.752%	$45.8435	$45.84	$45.85	$45.80
Purchase #4	$26.82	11.368%	$29.8689	$29.87	$29.85	$29.90
Purchase #5	$240.84	6.621%	$256.786	$256.79	$256.80	$256.80
Purchase #6	$42.31	9.459%	$46.3121	$46.31	$46.30	$46.30
Purchase #7	$138.59	12.778%	$156.299	$156.30	$156.30	$156.30
7 purchase totals =	$550.08		$599.4260	$599.43	$599.45	$599.40