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	$103.71	5.861%	$109.7884	$109.79	$109.80	$109.80
Purchase #2	$210.79	4.845%	$221.0028	$221.00	$221.00	$221.00
Purchase #3	$232.38	6.671%	$247.8821	$247.88	$247.90	$247.90
Purchase #4	$46.32	10.115%	$51.0053	$51.01	$51.00	$51.00
Purchase #5	$81.58	11.113%	$90.646	$90.65	$90.65	$90.60
Purchase #6	$41.52	5.121%	$43.6462	$43.65	$43.65	$43.60
Purchase #7	$22.43	13.761%	$25.5166	$25.52	$25.50	$25.50
7 purchase totals =	$738.73		$789.4874	$789.50	$789.50	$789.40