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	$56.46	13.778%	$64.2391	$64.24	$64.25	$64.20
Purchase #2	$140.80	6.802%	$150.3772	$150.38	$150.40	$150.40
Purchase #3	$220.28	7.290%	$236.3384	$236.34	$236.35	$236.30
Purchase #4	$107.35	3.663%	$111.2822	$111.28	$111.30	$111.30
Purchase #5	$78.31	6.367%	$83.296	$83.30	$83.30	$83.30
Purchase #6	$92.79	5.592%	$97.9788	$97.98	$98.00	$98.00
Purchase #7	$118.91	4.758%	$124.5677	$124.57	$124.55	$124.60
7 purchase totals =	$814.90		$868.0794	$868.09	$868.15	$868.10