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	$226.34	10.271%	$249.5874	$249.59	$249.60	$249.60
Purchase #2	$20.61	3.407%	$21.3122	$21.31	$21.30	$21.30
Purchase #3	$142.34	4.607%	$148.8976	$148.90	$148.90	$148.90
Purchase #4	$85.38	12.498%	$96.0508	$96.05	$96.05	$96.10
Purchase #5	$110.49	5.767%	$116.862	$116.86	$116.85	$116.90
Purchase #6	$31.95	5.356%	$33.6612	$33.66	$33.65	$33.70
Purchase #7	$120.38	11.495%	$134.2177	$134.22	$134.20	$134.20
7 purchase totals =	$737.49		$800.5889	$800.59	$800.55	$800.70