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	$199.52	12.829%	$225.1164	$225.12	$225.10	$225.10
Purchase #2	$245.65	4.353%	$256.3431	$256.34	$256.35	$256.30
Purchase #3	$43.86	3.613%	$45.4447	$45.44	$45.45	$45.40
Purchase #4	$34.51	3.132%	$35.5909	$35.59	$35.60	$35.60
Purchase #5	$59.91	6.628%	$63.8808	$63.88	$63.90	$63.90
Purchase #6	$142.93	9.234%	$156.1282	$156.13	$156.15	$156.10
Purchase #7	$111.43	8.866%	$121.3094	$121.31	$121.30	$121.30
7 purchase totals =	$837.81		$903.8135	$903.81	$903.85	$903.70