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	$134.35	10.364%	$148.274	$148.27	$148.25	$148.30
Purchase #2	$121.61	8.664%	$132.1463	$132.15	$132.15	$132.10
Purchase #3	$116.52	7.770%	$125.5736	$125.57	$125.55	$125.60
Purchase #4	$78.32	6.682%	$83.5533	$83.55	$83.55	$83.60
Purchase #5	$237.91	12.686%	$268.0913	$268.09	$268.10	$268.10
Purchase #6	$138.28	12.573%	$155.6659	$155.67	$155.65	$155.70
Purchase #7	$173.79	7.641%	$187.0693	$187.07	$187.05	$187.10
7 purchase totals =	$1,000.78		$1,100.3737	$1,100.37	$1,100.30	$1,100.50