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	$48.60	11.357%	$54.1195	$54.12	$54.10	$54.10
Purchase #2	$94.54	13.276%	$107.0911	$107.09	$107.10	$107.10
Purchase #3	$167.52	9.129%	$182.8129	$182.81	$182.80	$182.80
Purchase #4	$95.97	9.686%	$105.2657	$105.27	$105.25	$105.30
Purchase #5	$249.35	8.428%	$270.3652	$270.37	$270.35	$270.40
Purchase #6	$121.50	4.698%	$127.2081	$127.21	$127.20	$127.20
Purchase #7	$67.48	7.334%	$72.429	$72.43	$72.45	$72.40
7 purchase totals =	$844.96		$919.2915	$919.30	$919.25	$919.30