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	$121.61	4.456%	$127.0289	$127.03	$127.05	$127.00
Purchase #2	$60.81	6.644%	$64.8502	$64.85	$64.85	$64.90
Purchase #3	$41.71	13.650%	$47.4034	$47.40	$47.40	$47.40
Purchase #4	$93.59	11.450%	$104.3061	$104.31	$104.30	$104.30
Purchase #5	$23.35	6.562%	$24.8822	$24.88	$24.90	$24.90
Purchase #6	$29.97	3.825%	$31.1164	$31.12	$31.10	$31.10
Purchase #7	$147.54	7.718%	$158.9271	$158.93	$158.95	$158.90
7 purchase totals =	$518.58		$558.5143	$558.52	$558.55	$558.50