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	$210.85	11.209%	$234.4842	$234.48	$234.50	$234.50
Purchase #2	$164.49	10.209%	$181.2828	$181.28	$181.30	$181.30
Purchase #3	$142.83	11.369%	$159.0683	$159.07	$159.05	$159.10
Purchase #4	$152.77	4.644%	$159.8646	$159.86	$159.85	$159.90
Purchase #5	$132.91	5.300%	$139.9542	$139.95	$139.95	$140.00
Purchase #6	$116.82	11.391%	$130.127	$130.13	$130.15	$130.10
Purchase #7	$78.67	6.685%	$83.9291	$83.93	$83.95	$83.90
7 purchase totals =	$999.34		$1,088.7102	$1,088.70	$1,088.75	$1,088.80