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	$13.27	3.728%	$13.7647	$13.76	$13.75	$13.80
Purchase #2	$106.52	4.527%	$111.3422	$111.34	$111.35	$111.30
Purchase #3	$176.43	7.444%	$189.5634	$189.56	$189.55	$189.60
Purchase #4	$196.36	12.376%	$220.6615	$220.66	$220.65	$220.70
Purchase #5	$52.86	7.206%	$56.6691	$56.67	$56.65	$56.70
Purchase #6	$106.59	11.275%	$118.608	$118.61	$118.60	$118.60
Purchase #7	$68.30	5.767%	$72.2389	$72.24	$72.25	$72.20
7 purchase totals =	$720.33		$782.8478	$782.84	$782.80	$782.90