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	$114.83	11.484%	$128.0171	$128.02	$128.00	$128.00
Purchase #2	$122.45	13.741%	$139.2759	$139.28	$139.30	$139.30
Purchase #3	$76.33	8.369%	$82.7181	$82.72	$82.70	$82.70
Purchase #4	$21.76	13.583%	$24.7157	$24.72	$24.70	$24.70
Purchase #5	$92.36	6.732%	$98.5777	$98.58	$98.60	$98.60
Purchase #6	$159.60	4.839%	$167.323	$167.32	$167.30	$167.30
Purchase #7	$185.95	5.669%	$196.4915	$196.49	$196.50	$196.50
7 purchase totals =	$773.28		$837.1190	$837.13	$837.10	$837.10