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	$42.69	12.233%	$47.9123	$47.91	$47.90	$47.90
Purchase #2	$96.71	12.296%	$108.6015	$108.60	$108.60	$108.60
Purchase #3	$89.95	11.716%	$100.4885	$100.49	$100.50	$100.50
Purchase #4	$122.54	11.646%	$136.811	$136.81	$136.80	$136.80
Purchase #5	$56.71	6.745%	$60.5351	$60.54	$60.55	$60.50
Purchase #6	$6.92	5.377%	$7.2921	$7.29	$7.30	$7.30
Purchase #7	$162.35	3.250%	$167.6264	$167.63	$167.65	$167.60
7 purchase totals =	$577.87		$629.2669	$629.27	$629.30	$629.20