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	$70.39	12.378%	$79.1029	$79.10	$79.10	$79.10
Purchase #2	$123.90	6.168%	$131.5422	$131.54	$131.55	$131.50
Purchase #3	$68.39	11.772%	$76.4409	$76.44	$76.45	$76.40
Purchase #4	$226.47	5.433%	$238.7741	$238.77	$238.75	$238.80
Purchase #5	$97.56	9.782%	$107.1033	$107.10	$107.10	$107.10
Purchase #6	$103.53	7.561%	$111.3579	$111.36	$111.35	$111.40
Purchase #7	$131.47	13.749%	$149.5458	$149.55	$149.55	$149.50
7 purchase totals =	$821.71		$893.8671	$893.86	$893.85	$893.80